🕷️ Crawler Inspector

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Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 101 (from laksa046)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa101.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://www.sfgate.com/shopping/article/PCR-vs-antigen-testing-what-s-the-difference-16765004.php\')), getAhrefsUnparsedNoserviceFromURL(\'https://www.sfgate.com/shopping/article/PCR-vs-antigen-testing-what-s-the-difference-16765004.php\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/www.sfgate.com\/shopping\/article\/PCR-vs-antigen-testing-what-s-the-difference-16765004.php","crawl_time":1775691525,"first_indexed_time":1641859572,"http_code":200,"src_unparsed":"com,sfgate!www,\/shopping\/article\/PCR-vs-antigen-testing-what-s-the-difference-16765004.php s443","src_root_hash":"9965634055219334301","history_drop_reason":null,"meta_title":"PCR vs. antigent testing: what's the difference?","meta_descriptions":["We spoke to experts to get real answers."],"attrs_boilerpipe_text":"DxTerity\nTwo years into the pandemic, we’re getting some solid testing options finally available on a widespread basis — never mind that shortage of at-home rapid antigen tests (RATs) that happened over the duration between Christmas and New Year’s. But PCR tests and RATs remain on the pricey side, so you don’t want to spend your money on the wrong kind of test for the wrong reasons. \n“PCR (polymerase chain reaction) and antigen tests — both of which typically use nasal swabs to collect samples — differ in detection methods, processing, and turnaround times,” says Dr. Ariella Morrow from Sameday Health, a personalized healthcare provider with nationwide covid-testing clinic and services. :\nWe’ve spoken to her and other medical experts about the differences between a PCR and RAT—as well as what situations you should use either kind of test for. \nWhat is the difference between a PCR and an antigen test? \nEach test uses a different process to detect the presence of Covid-19 in your body, with PCR tests taking a super-thorough look — if you have Covid, there’s a greater chance you’ll test positive with a PCR test than with a rapid antigen test, says Erica Susky, an infection control practitioner in hospital epidemiology, making them the best accessible way to tell if you have COVID or not.  \n“PCRs, a molecular test, look for the virus’ genetic material within the specimens sample, which is then processed in a lab (often resulting in a longer turnaround time),” says Morrow. “These are the most accurate tests available due to their high sensitivity, and thus, the most widely used form of covid test by the medical community. Meanwhile, antigen tests search for a piece of the virus’ protein in the sample, which can then be analyzed by a healthcare professional in real-time or at home.”\nRapid antigen tests (RAT) are easier to perform because anyone can do one at home and it’s faster obtain results, says Susky. They usually take about 15 to 30 minutes for results. \nBut there is a downside.\n“Although antigen tests typically provide results in under fifteen minutes,\" says Marrow, \"they are more likely to yield false-negative results due to lesser sensitivity, especially for those that are asymptomatic.” \nWhile most people perform their own antigen tests, PCR tests are almost always administered by someone else, with samples sent to a lab for detection and analysis. “This test takes more time as it is required to be done by trained laboratory professionals,” says Susky. “Wait times can be as much as 72 hours for PCR results.\"\nWhat’s the science behind PCR and antigen tests? \n“PCR (or polymerase chain reaction) amplifies targeted regions of a genome,” says Erica Susky, an infection control practitioner in hospital epidemiology. “In the case of SARS-CoV-2, as the viral genome is made of RNA, there are pieces of RNA primer made in the laboratory designed to bind to areas of the SARS-CoV-2 sequence with the intention of amplifying them. The chain reaction entails temperature cycling that allow the targeted pieces of SARS-CoV-2 to be amplified so they will then be easily detected, usually with fluorescent dyes.” \nSince this involves amplification of parts of the SARS-CoV-2 virus, “RATs work by binding antigens to antibodies,” says Susky. “Antibodies are made by the immune system and function by binding select targets. One gets a nasal or throat specimen and puts it in a liquid buffer”— i.e. you swab your nose and then swirl it around some liquid that comes with the test kit. “The buffer is flooded onto the RAT slide,” she says. “The RAT slide contains SARS-CoV-2 antigens bound to a color marker.”\nIf you have Covid, then the antibodies from the virus bind to the color-marked antigen in the test and you’ll see a colored band. \nPCR vs. antigen: Which one is more accurate? \nPCR tests are ultimately the more accurate way to tell if you have COVID-19, but antigen tests are a great first line of defense if you think you have symptoms. It's best to use PCR tests, rather than antigen tests, before higher-risk situations for you and others or when legally required, like before a flight.\nSusky says PCR testing “is much more sensitive than antigen testing. What this means is that with someone who has COVID-19, there is a greater chance that they will test positive by PCR than with the antigen test, or there are fewer chances of false negative results.” \nOn the other hand, “rapid antigen tests are not as sensitive as PCR — there’s a higher chance of testing negative when one may in fact have COVID-19, but they are quite specific,” Susky says. “Something with a good specificity means that a positive result has a high probability of the presence of disease. Therefore, if one tests positive by RAT it is safe to say they have COVID-19 and should isolate at home.” \nWhere can you buy antigen and PCR tests?\nBecause PCR tests require the use of a lab, the easiest way to get a PCR test is to book it with a test provider — just be prepared to fork out some money for it. Antigen tests are now widely available and come in at\nless than $18 for two\non sites like Amazon, which isn’t cheap but a lot better than spreading COVID-19. \nJan 10, 2022\n|\nUpdated\nJan 11, 2022 8:34 a.m.\nFreelance Writer\nKrystin Arneson is a freelance writer and editor based in Europe (and frequently elsewhere). When not covering shopping, she's writing about travel, wine, or culture.","attrs_markdown":"SF Gate Logo\n\nHearst Newspapers Logo\n\n[Skip to main content](https:\/\/www.sfgate.com\/shopping\/article\/PCR-vs-antigen-testing-what-s-the-difference-16765004.php#content)\n\n[CA MINI CROSSWORD](https:\/\/www.sfgate.com\/california-mini-crossword-puzzle-puzzmo\/?utm_source=masthead&utm_medium=button&utm_campaign=campaignname&utm_term=camini)\n\n[Home](https:\/\/www.sfgate.com\/)\n\n- [Classifieds](http:\/\/sfc.ipublishmarketplace.com\/sf-marketplace\/)\n- [Standards & Practices](https:\/\/www.sfgate.com\/standards\/)\n- [Advertise With Us](https:\/\/marketing.sfgate.com\/advertise-with-us-today?utm_source=sfgate)\n- [Privacy Notice](https:\/\/www.sfgate.com\/privacy\/)\n- [Terms of Use](https:\/\/www.sfgate.com\/terms\/)\n- [Ad Choices](http:\/\/www.aboutads.info\/choices\/)\n- [Your Privacy Choices](https:\/\/www.sfgate.com\/yourdata\/)\n\n[About SFGATE](https:\/\/www.sfgate.com\/home\/article\/about-sfgate-15613713.php)\n\n[Careers](https:\/\/eevd.fa.us6.oraclecloud.com\/hcmUI\/CandidateExperience\/en\/sites\/CX_11007\/requisitions?keyword=SFGATE&mode=location)\n\n[Contact SFGATE](https:\/\/www.sfgate.com\/home\/article\/sfgate-staff-15734829.php)\n\n[Newsletters](https:\/\/link.sfgate.com\/join\/signup-sfgate)\n\n[News](https:\/\/www.sfgate.com\/news\/)\n\n- [Bay Area](https:\/\/www.sfgate.com\/bayarea\/)\n- [California Wildfires](https:\/\/www.sfgate.com\/california-wildfires\/)\n- [Education](https:\/\/www.sfgate.com\/education\/)\n- [North Coast](https:\/\/www.sfgate.com\/northcoast\/)\n- [Politics](https:\/\/www.sfgate.com\/politics\/)\n- [Weather](https:\/\/www.sfgate.com\/weather\/)\n\n[Sports](https:\/\/www.sfgate.com\/sports\/)\n\n- [49ers](https:\/\/www.sfgate.com\/49ers\/)\n- [Giants](https:\/\/www.sfgate.com\/giants\/)\n- [A's](https:\/\/www.sfgate.com\/athletics\/)\n- [Warriors](https:\/\/www.sfgate.com\/warriors\/)\n\n[Bay Area](https:\/\/www.sfgate.com\/local\/)\n\n- [SF History](https:\/\/www.sfgate.com\/sfhistory\/)\n\n[Travel](https:\/\/www.sfgate.com\/travel\/)\n\n- [California Parks](https:\/\/www.sfgate.com\/california-parks\/)\n- [Central Coast](https:\/\/www.sfgate.com\/centralcoast\/)\n- [Disneyland](https:\/\/www.sfgate.com\/disneyland\/)\n- [Hawaii](https:\/\/www.sfgate.com\/hawaii\/)\n- [Monterey-Carmel](https:\/\/www.sfgate.com\/monterey-carmel\/)\n- [Tahoe](https:\/\/www.sfgate.com\/renotahoe\/)\n- [Wine Country](https:\/\/www.sfgate.com\/winecountry\/)\n\n[Food + Drink](https:\/\/www.sfgate.com\/food\/)\n\n[Culture](https:\/\/www.sfgate.com\/sf-culture\/)\n\n[Tech](https:\/\/www.sfgate.com\/tech\/)\n\n[Los Angeles](https:\/\/www.sfgate.com\/la\/)\n\n[California](https:\/\/www.sfgate.com\/california\/)\n\n[National Parks](https:\/\/www.sfgate.com\/national-parks\/)\n\n[Real Estate](https:\/\/www.sfgate.com\/realestate\/)\n\n- [New Homes](https:\/\/www.sfgate.com\/newhomes\/)\n- [(Virtual) Open Homes](https:\/\/www.sfgate.com\/openhomes\/)\n- [Luxury](https:\/\/www.sfgate.com\/luxuryhomes\/)\n- [Rentals](https:\/\/www.sfgate.com\/rentals\/)\n- [Place a Real Estate Ad](https:\/\/myagentads.hearst.com\/realestate\/sfchronicle\/index.html)\n- [Neighborhood Guides](https:\/\/www.sfgate.com\/sfneighborhoods\/)\n- [Home & Garden](https:\/\/www.sfgate.com\/homeandgarden\/)\n- [Movers](https:\/\/www.sfgate.com\/realestate\/movers\/)\n\n[Obits](https:\/\/www.legacy.com\/obituaries\/sfgate?ipid=desktopnav9-12)\n\n- [Obituaries](https:\/\/www.legacy.com\/obituaries\/sfgate?ipid=desktopnav9-12)\n- [Place an Obituary](https:\/\/ezads.hearst.com\/obits\/sfchronicle\/index.html)\n\n[Best Of](https:\/\/www.sfgate.com\/best\/)\n\n[Shopping](https:\/\/www.sfgate.com\/shopping\/)\n\n[Puzzles](https:\/\/www.sfgate.com\/puzzles\/)\n\n[Sponsor Content](https:\/\/www.sfgate.com\/sponsoredarticles\/lifestyle\/)\n\n- [StoryStudio](https:\/\/storystudio.sfgate.com\/)\n- [Paid Press Releases](https:\/\/www.sfgate.com\/business\/press-releases\/)\n- [Senior Living](https:\/\/www.sfgate.com\/senior-living\/)\n- [Sponsor Content: Business](https:\/\/www.sfgate.com\/sponsoredarticles\/business\/)\n\n[SF Gate Logo](https:\/\/www.sfgate.com\/)\n\n[CA MINI CROSSWORD](https:\/\/www.sfgate.com\/california-mini-crossword-puzzle-puzzmo\/?utm_source=masthead&utm_medium=button&utm_campaign=campaignname&utm_term=camini)\n\nWe handpick every product we feature. We may be compensated or earn commission from the links on this page.\n\n[Shopping](https:\/\/www.sfgate.com\/shopping\/)\n\n# PCR vs. antigen testing: what’s the difference, and what should you buy?\n## We spoke to experts to get real answers.\nBy [Krystin Arneson](https:\/\/www.sfgate.com\/author\/krystin-arneson\/), Freelance Writer\n\nUpdated\n\nJan 11, 2022 8:34 a.m.\n\n![Saliva At-Home Collection Kit]()\n\n[Saliva At-Home Collection Kit](https:\/\/www.walmart.com\/ip\/DxTerity-SARS-CoV-2-RT-PCR-CE-Test-COVID-19-Saliva-At-Home-Collection-Kit\/518633039?selected=true&irgwc=1&sourceid=imp_SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&veh=aff&wmlspartner=imp_10078&clickid=SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&sharedid=sfgate.com&affiliates_ad_id=612734&campaign_id=9383)\n\nDxTerity\n\nTwo years into the pandemic, we’re getting some solid testing options finally available on a widespread basis — never mind that shortage of at-home rapid antigen tests (RATs) that happened over the duration between Christmas and New Year’s. But PCR tests and RATs remain on the pricey side, so you don’t want to spend your money on the wrong kind of test for the wrong reasons.\n\n![](https:\/\/cdn-channels-pixel.ex.co\/events\/0012000001fxZm9AAE?integrationType=DEFAULT&template=design%2Farticle%2Fplatypus_two_column.tpl)\n\n“PCR (polymerase chain reaction) and antigen tests — both of which typically use nasal swabs to collect samples — differ in detection methods, processing, and turnaround times,” says Dr. Ariella Morrow from Sameday Health, a personalized healthcare provider with nationwide covid-testing clinic and services. :\n\nWe’ve spoken to her and other medical experts about the differences between a PCR and RAT—as well as what situations you should use either kind of test for.\n\n## What is the difference between a PCR and an antigen test?\nEach test uses a different process to detect the presence of Covid-19 in your body, with PCR tests taking a super-thorough look — if you have Covid, there’s a greater chance you’ll test positive with a PCR test than with a rapid antigen test, says Erica Susky, an infection control practitioner in hospital epidemiology, making them the best accessible way to tell if you have COVID or not.\n\n**[PCR CE Test - COVID-19 Saliva At-Home Collection Kit](https:\/\/www.walmart.com\/ip\/DxTerity-SARS-CoV-2-RT-PCR-CE-Test-COVID-19-Saliva-At-Home-Collection-Kit\/518633039?selected=true&irgwc=1&sourceid=imp_SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&veh=aff&wmlspartner=imp_10078&clickid=SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&sharedid=sfgate.com&affiliates_ad_id=612734&campaign_id=9383)**\n\n[![PCR CE Test - COVID-19 Saliva At-Home Collection Kit]()](https:\/\/www.walmart.com\/ip\/518633039?selected=true)\n\nDxTerity\n\n[PCR CE Test - COVID-19 Saliva At-Home Collection Kit](https:\/\/www.walmart.com\/ip\/518633039?selected=true)\n\n[\\$95.00 at walmart.com](https:\/\/www.walmart.com\/ip\/518633039?selected=true)\n\n“PCRs, a molecular test, look for the virus’ genetic material within the specimens sample, which is then processed in a lab (often resulting in a longer turnaround time),” says Morrow. “These are the most accurate tests available due to their high sensitivity, and thus, the most widely used form of covid test by the medical community. Meanwhile, antigen tests search for a piece of the virus’ protein in the sample, which can then be analyzed by a healthcare professional in real-time or at home.”\n\n[**On\/Go at-Home COVID-19 Rapid Antigen Self-Test**](https:\/\/www.amazon.com\/dp\/B09FP6HWCV?ots=1&slotNum=4&imprToken=02bf22e3-a10f-acf9-b2a&tag=hearstnp-sfg-20&th=1&ascsubtag=wcm~16765004~1775691525~inl~~~~~~~B09FP6HWCV)\n\n[![at-Home COVID-19 Rapid Antigen Test]()](https:\/\/www.amazon.com\/dp\/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV)\n\nON\/GO\n\n[at-Home COVID-19 Rapid Antigen Test](https:\/\/www.amazon.com\/dp\/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV)\n\n[\\$20.00 at amazon.com](https:\/\/www.amazon.com\/dp\/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV)\n\nRapid antigen tests (RAT) are easier to perform because anyone can do one at home and it’s faster obtain results, says Susky. They usually take about 15 to 30 minutes for results.\n\nBut there is a downside.\n\n“Although antigen tests typically provide results in under fifteen minutes,\" says Marrow, \"they are more likely to yield false-negative results due to lesser sensitivity, especially for those that are asymptomatic.”\n\nWhile most people perform their own antigen tests, PCR tests are almost always administered by someone else, with samples sent to a lab for detection and analysis. “This test takes more time as it is required to be done by trained laboratory professionals,” says Susky. “Wait times can be as much as 72 hours for PCR results.\"\n\n## What’s the science behind PCR and antigen tests?\n“PCR (or polymerase chain reaction) amplifies targeted regions of a genome,” says Erica Susky, an infection control practitioner in hospital epidemiology. “In the case of SARS-CoV-2, as the viral genome is made of RNA, there are pieces of RNA primer made in the laboratory designed to bind to areas of the SARS-CoV-2 sequence with the intention of amplifying them. The chain reaction entails temperature cycling that allow the targeted pieces of SARS-CoV-2 to be amplified so they will then be easily detected, usually with fluorescent dyes.”\n\nSince this involves amplification of parts of the SARS-CoV-2 virus, “RATs work by binding antigens to antibodies,” says Susky. “Antibodies are made by the immune system and function by binding select targets. One gets a nasal or throat specimen and puts it in a liquid buffer”— i.e. you swab your nose and then swirl it around some liquid that comes with the test kit. “The buffer is flooded onto the RAT slide,” she says. “The RAT slide contains SARS-CoV-2 antigens bound to a color marker.”\n\nIf you have Covid, then the antibodies from the virus bind to the color-marked antigen in the test and you’ll see a colored band.\n\n## PCR vs. antigen: Which one is more accurate?\nPCR tests are ultimately the more accurate way to tell if you have COVID-19, but antigen tests are a great first line of defense if you think you have symptoms. It's best to use PCR tests, rather than antigen tests, before higher-risk situations for you and others or when legally required, like before a flight.\n\nSusky says PCR testing “is much more sensitive than antigen testing. What this means is that with someone who has COVID-19, there is a greater chance that they will test positive by PCR than with the antigen test, or there are fewer chances of false negative results.”\n\nOn the other hand, “rapid antigen tests are not as sensitive as PCR — there’s a higher chance of testing negative when one may in fact have COVID-19, but they are quite specific,” Susky says. “Something with a good specificity means that a positive result has a high probability of the presence of disease. Therefore, if one tests positive by RAT it is safe to say they have COVID-19 and should isolate at home.”\n\n## Where can you buy antigen and PCR tests?\nBecause PCR tests require the use of a lab, the easiest way to get a PCR test is to book it with a test provider — just be prepared to fork out some money for it. Antigen tests are now widely available and come in at [less than \\$18 for two](https:\/\/www.amazon.com\/iHealth-COVID-19-Authorized-Non-invasive-Discomfort\/dp\/B09KZ6TBNY\/ref=sr_1_5?crid=37ZR24MZK5OHW&keywords=PCR+covid+test&qid=1640728076&sprefix=pcr+covid+test%2Caps%2C110&sr=8-5&tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~inl~~~~~~~B09KZ6TBNY) on sites like Amazon, which isn’t cheap but a lot better than spreading COVID-19.\n\nJan 10, 2022\n\n\\|Updated\n\nJan 11, 2022 8:34 a.m.\n\n[Krystin Arneson](https:\/\/www.sfgate.com\/author\/krystin-arneson\/)\n\nFreelance Writer\n\nKrystin Arneson is a freelance writer and editor based in Europe (and frequently elsewhere). When not covering shopping, she's writing about travel, wine, or culture.\n\n[Best Of](https:\/\/www.sfgate.com\/best)\n\nBest Of\n\n[Top-rated appliance repair companies in the Bay Area](https:\/\/www.sfgate.com\/best\/map\/top-rated-appliance-repair-companies-bay-area\/)\n\n[Call these pros with your dishwasher's on the fritz.](https:\/\/www.sfgate.com\/best\/map\/top-rated-appliance-repair-companies-bay-area\/)\n\n[![Top-rated appliance repair companies in the Bay Area]()](https:\/\/www.sfgate.com\/best\/map\/top-rated-appliance-repair-companies-bay-area\/)\n\nBest Of\n\n[Why homeowners use USA Bath for bathroom upgrades](https:\/\/www.sfgate.com\/best\/map\/best-bathroom-remodeling-companies-sacramento\/#usabath)\n\n[If your bathroom feels outdated, USA Bath specializes in remodels. 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The accessory has AC outlets, USB ports, and two retractable USB-C cables.](https:\/\/www.sfgate.com\/shopping\/article\/anker-nano-charging-station-power-strip-deal-22193401.php)\n\n[![Back down to its all-time low price.]()](https:\/\/www.sfgate.com\/shopping\/article\/anker-nano-charging-station-power-strip-deal-22193401.php)\n\n[Shopping](https:\/\/www.sfgate.com\/shopping\/)\n\n[Nomadix’s new Collab with Brooks arrives just in time for trail running season](https:\/\/www.sfgate.com\/shopping\/article\/brooks-nomadix-limited-edition-running-shoe-22096310.php)\n\n[Brooks and Nomadix just dropped a limited-edition Ghost Trail shoe built for summer miles, with grippy traction and responsive cushioning.](https:\/\/www.sfgate.com\/shopping\/article\/brooks-nomadix-limited-edition-running-shoe-22096310.php)\n\n[![Snag this limited edition Brooks x Nomadix Collection shoe while it's still 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trash and recycling bins start at \\$245 and ditch the typical eyesore design with slim, modern options that actually look good in your kitchen.](https:\/\/www.sfgate.com\/shopping\/article\/caraway-trash-recycling-bins-22185369.php)\n\n[![Caraway’s new trash and recycling bins come in muted colors and slim shapes that are easier on the eyes than standard kitchen cans.]()](https:\/\/www.sfgate.com\/shopping\/article\/caraway-trash-recycling-bins-22185369.php)\n\nMost Popular\n\n1\\.\n\n[California made them rich on paper and now they’re stuck in place](https:\/\/www.sfgate.com\/california\/article\/gains-taxes-california-housing-22183896.php)\n\n2\\.\n\n[SF Giants manager reveals team has had 3 clubhouse incidents in first 10 games](https:\/\/www.sfgate.com\/giants\/article\/giants-tony-vitello-incidents-22193831.php)\n\n3\\.\n\n[Emeryville woman's dream cookie business has become a 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But PCR tests and RATs remain on the pricey side, so you don’t want to spend your money on the wrong kind of test for the wrong reasons.\n\n“PCR (polymerase chain reaction) and antigen tests — both of which typically use nasal swabs to collect samples — differ in detection methods, processing, and turnaround times,” says Dr. Ariella Morrow from Sameday Health, a personalized healthcare provider with nationwide covid-testing clinic and services. :\n\nWe’ve spoken to her and other medical experts about the differences between a PCR and RAT—as well as what situations you should use either kind of test for.\n\nWhat is the difference between a PCR and an antigen test?\n\nEach test uses a different process to detect the presence of Covid-19 in your body, with PCR tests taking a super-thorough look — if you have Covid, there’s a greater chance you’ll test positive with a PCR test than with a rapid antigen test, says Erica Susky, an infection control practitioner in hospital epidemiology, making them the best accessible way to tell if you have COVID or not.\n\n[![PCR CE Test - COVID-19 Saliva At-Home Collection Kit]()](https:\/\/www.walmart.com\/ip\/518633039?selected=true)\n\n“PCRs, a molecular test, look for the virus’ genetic material within the specimens sample, which is then processed in a lab (often resulting in a longer turnaround time),” says Morrow. “These are the most accurate tests available due to their high sensitivity, and thus, the most widely used form of covid test by the medical community. Meanwhile, antigen tests search for a piece of the virus’ protein in the sample, which can then be analyzed by a healthcare professional in real-time or at home.”\n\n[![at-Home COVID-19 Rapid Antigen Test]()](https:\/\/www.amazon.com\/dp\/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV)\n\nRapid antigen tests (RAT) are easier to perform because anyone can do one at home and it’s faster obtain results, says Susky. They usually take about 15 to 30 minutes for results.\n\nBut there is a downside.\n\n“Although antigen tests typically provide results in under fifteen minutes,\" says Marrow, \"they are more likely to yield false-negative results due to lesser sensitivity, especially for those that are asymptomatic.”\n\nWhile most people perform their own antigen tests, PCR tests are almost always administered by someone else, with samples sent to a lab for detection and analysis. “This test takes more time as it is required to be done by trained laboratory professionals,” says Susky. “Wait times can be as much as 72 hours for PCR results.\"\n\nWhat’s the science behind PCR and antigen tests?\n\n“PCR (or polymerase chain reaction) amplifies targeted regions of a genome,” says Erica Susky, an infection control practitioner in hospital epidemiology. “In the case of SARS-CoV-2, as the viral genome is made of RNA, there are pieces of RNA primer made in the laboratory designed to bind to areas of the SARS-CoV-2 sequence with the intention of amplifying them. The chain reaction entails temperature cycling that allow the targeted pieces of SARS-CoV-2 to be amplified so they will then be easily detected, usually with fluorescent dyes.”\n\nSince this involves amplification of parts of the SARS-CoV-2 virus, “RATs work by binding antigens to antibodies,” says Susky. “Antibodies are made by the immune system and function by binding select targets. One gets a nasal or throat specimen and puts it in a liquid buffer”— i.e. you swab your nose and then swirl it around some liquid that comes with the test kit. “The buffer is flooded onto the RAT slide,” she says. “The RAT slide contains SARS-CoV-2 antigens bound to a color marker.”\n\nIf you have Covid, then the antibodies from the virus bind to the color-marked antigen in the test and you’ll see a colored band.\n\nPCR vs. antigen: Which one is more accurate?\n\nPCR tests are ultimately the more accurate way to tell if you have COVID-19, but antigen tests are a great first line of defense if you think you have symptoms. It's best to use PCR tests, rather than antigen tests, before higher-risk situations for you and others or when legally required, like before a flight.\n\nSusky says PCR testing “is much more sensitive than antigen testing. What this means is that with someone who has COVID-19, there is a greater chance that they will test positive by PCR than with the antigen test, or there are fewer chances of false negative results.”\n\nOn the other hand, “rapid antigen tests are not as sensitive as PCR — there’s a higher chance of testing negative when one may in fact have COVID-19, but they are quite specific,” Susky says. “Something with a good specificity means that a positive result has a high probability of the presence of disease. Therefore, if one tests positive by RAT it is safe to say they have COVID-19 and should isolate at home.”\n\nWhere can you buy antigen and PCR tests?\n\nBecause PCR tests require the use of a lab, the easiest way to get a PCR test is to book it with a test provider — just be prepared to fork out some money for it. Antigen tests are now widely available and come in at [less than \\$18 for two](https:\/\/www.amazon.com\/iHealth-COVID-19-Authorized-Non-invasive-Discomfort\/dp\/B09KZ6TBNY\/ref=sr_1_5?crid=37ZR24MZK5OHW&keywords=PCR+covid+test&qid=1640728076&sprefix=pcr+covid+test%2Caps%2C110&sr=8-5&tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~inl~~~~~~~B09KZ6TBNY) on sites like Amazon, which isn’t cheap but a lot better than spreading COVID-19.\n\nJan 10, 2022 \\|Updated Jan 11, 2022 8:34 a.m.\n\nFreelance Writer\n\nKrystin Arneson is a freelance writer and editor based in Europe (and frequently elsewhere). When not covering shopping, she's writing about travel, wine, or culture.","meta_canonical":null}

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URL	https://www.sfgate.com/shopping/article/PCR-vs-antigen-testing-what-s-the-difference-16765004.php
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Meta Title	PCR vs. antigent testing: what's the difference?
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Boilerpipe Text	DxTerity Two years into the pandemic, we’re getting some solid testing options finally available on a widespread basis — never mind that shortage of at-home rapid antigen tests (RATs) that happened over the duration between Christmas and New Year’s. But PCR tests and RATs remain on the pricey side, so you don’t want to spend your money on the wrong kind of test for the wrong reasons. “PCR (polymerase chain reaction) and antigen tests — both of which typically use nasal swabs to collect samples — differ in detection methods, processing, and turnaround times,” says Dr. Ariella Morrow from Sameday Health, a personalized healthcare provider with nationwide covid-testing clinic and services. : We’ve spoken to her and other medical experts about the differences between a PCR and RAT—as well as what situations you should use either kind of test for. What is the difference between a PCR and an antigen test? Each test uses a different process to detect the presence of Covid-19 in your body, with PCR tests taking a super-thorough look — if you have Covid, there’s a greater chance you’ll test positive with a PCR test than with a rapid antigen test, says Erica Susky, an infection control practitioner in hospital epidemiology, making them the best accessible way to tell if you have COVID or not. “PCRs, a molecular test, look for the virus’ genetic material within the specimens sample, which is then processed in a lab (often resulting in a longer turnaround time),” says Morrow. “These are the most accurate tests available due to their high sensitivity, and thus, the most widely used form of covid test by the medical community. Meanwhile, antigen tests search for a piece of the virus’ protein in the sample, which can then be analyzed by a healthcare professional in real-time or at home.” Rapid antigen tests (RAT) are easier to perform because anyone can do one at home and it’s faster obtain results, says Susky. They usually take about 15 to 30 minutes for results. But there is a downside. “Although antigen tests typically provide results in under fifteen minutes," says Marrow, "they are more likely to yield false-negative results due to lesser sensitivity, especially for those that are asymptomatic.” While most people perform their own antigen tests, PCR tests are almost always administered by someone else, with samples sent to a lab for detection and analysis. “This test takes more time as it is required to be done by trained laboratory professionals,” says Susky. “Wait times can be as much as 72 hours for PCR results." What’s the science behind PCR and antigen tests? “PCR (or polymerase chain reaction) amplifies targeted regions of a genome,” says Erica Susky, an infection control practitioner in hospital epidemiology. “In the case of SARS-CoV-2, as the viral genome is made of RNA, there are pieces of RNA primer made in the laboratory designed to bind to areas of the SARS-CoV-2 sequence with the intention of amplifying them. The chain reaction entails temperature cycling that allow the targeted pieces of SARS-CoV-2 to be amplified so they will then be easily detected, usually with fluorescent dyes.” Since this involves amplification of parts of the SARS-CoV-2 virus, “RATs work by binding antigens to antibodies,” says Susky. “Antibodies are made by the immune system and function by binding select targets. One gets a nasal or throat specimen and puts it in a liquid buffer”— i.e. you swab your nose and then swirl it around some liquid that comes with the test kit. “The buffer is flooded onto the RAT slide,” she says. “The RAT slide contains SARS-CoV-2 antigens bound to a color marker.” If you have Covid, then the antibodies from the virus bind to the color-marked antigen in the test and you’ll see a colored band. PCR vs. antigen: Which one is more accurate? PCR tests are ultimately the more accurate way to tell if you have COVID-19, but antigen tests are a great first line of defense if you think you have symptoms. It's best to use PCR tests, rather than antigen tests, before higher-risk situations for you and others or when legally required, like before a flight. Susky says PCR testing “is much more sensitive than antigen testing. What this means is that with someone who has COVID-19, there is a greater chance that they will test positive by PCR than with the antigen test, or there are fewer chances of false negative results.” On the other hand, “rapid antigen tests are not as sensitive as PCR — there’s a higher chance of testing negative when one may in fact have COVID-19, but they are quite specific,” Susky says. “Something with a good specificity means that a positive result has a high probability of the presence of disease. Therefore, if one tests positive by RAT it is safe to say they have COVID-19 and should isolate at home.” Where can you buy antigen and PCR tests? Because PCR tests require the use of a lab, the easiest way to get a PCR test is to book it with a test provider — just be prepared to fork out some money for it. Antigen tests are now widely available and come in at less than $18 for two on sites like Amazon, which isn’t cheap but a lot better than spreading COVID-19. Jan 10, 2022 \| Updated Jan 11, 2022 8:34 a.m. Freelance Writer Krystin Arneson is a freelance writer and editor based in Europe (and frequently elsewhere). When not covering shopping, she's writing about travel, wine, or culture.
Markdown	SF Gate Logo Hearst Newspapers Logo [Skip to main content](https://www.sfgate.com/shopping/article/PCR-vs-antigen-testing-what-s-the-difference-16765004.php#content) [CA MINI CROSSWORD](https://www.sfgate.com/california-mini-crossword-puzzle-puzzmo/?utm_source=masthead&utm_medium=button&utm_campaign=campaignname&utm_term=camini) [Home](https://www.sfgate.com/) - [Classifieds](http://sfc.ipublishmarketplace.com/sf-marketplace/) - [Standards & Practices](https://www.sfgate.com/standards/) - [Advertise With Us](https://marketing.sfgate.com/advertise-with-us-today?utm_source=sfgate) - [Privacy Notice](https://www.sfgate.com/privacy/) - [Terms of Use](https://www.sfgate.com/terms/) - [Ad Choices](http://www.aboutads.info/choices/) - [Your Privacy Choices](https://www.sfgate.com/yourdata/) [About SFGATE](https://www.sfgate.com/home/article/about-sfgate-15613713.php) [Careers](https://eevd.fa.us6.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_11007/requisitions?keyword=SFGATE&mode=location) [Contact SFGATE](https://www.sfgate.com/home/article/sfgate-staff-15734829.php) [Newsletters](https://link.sfgate.com/join/signup-sfgate) [News](https://www.sfgate.com/news/) - [Bay Area](https://www.sfgate.com/bayarea/) - [California Wildfires](https://www.sfgate.com/california-wildfires/) - [Education](https://www.sfgate.com/education/) - [North Coast](https://www.sfgate.com/northcoast/) - [Politics](https://www.sfgate.com/politics/) - [Weather](https://www.sfgate.com/weather/) [Sports](https://www.sfgate.com/sports/) - [49ers](https://www.sfgate.com/49ers/) - [Giants](https://www.sfgate.com/giants/) - [A's](https://www.sfgate.com/athletics/) - [Warriors](https://www.sfgate.com/warriors/) [Bay Area](https://www.sfgate.com/local/) - [SF History](https://www.sfgate.com/sfhistory/) [Travel](https://www.sfgate.com/travel/) - [California Parks](https://www.sfgate.com/california-parks/) - [Central Coast](https://www.sfgate.com/centralcoast/) - [Disneyland](https://www.sfgate.com/disneyland/) - [Hawaii](https://www.sfgate.com/hawaii/) - [Monterey-Carmel](https://www.sfgate.com/monterey-carmel/) - [Tahoe](https://www.sfgate.com/renotahoe/) - [Wine Country](https://www.sfgate.com/winecountry/) [Food + Drink](https://www.sfgate.com/food/) [Culture](https://www.sfgate.com/sf-culture/) [Tech](https://www.sfgate.com/tech/) [Los Angeles](https://www.sfgate.com/la/) [California](https://www.sfgate.com/california/) [National Parks](https://www.sfgate.com/national-parks/) [Real Estate](https://www.sfgate.com/realestate/) - [New Homes](https://www.sfgate.com/newhomes/) - [(Virtual) Open Homes](https://www.sfgate.com/openhomes/) - [Luxury](https://www.sfgate.com/luxuryhomes/) - [Rentals](https://www.sfgate.com/rentals/) - [Place a Real Estate Ad](https://myagentads.hearst.com/realestate/sfchronicle/index.html) - [Neighborhood Guides](https://www.sfgate.com/sfneighborhoods/) - [Home & Garden](https://www.sfgate.com/homeandgarden/) - [Movers](https://www.sfgate.com/realestate/movers/) [Obits](https://www.legacy.com/obituaries/sfgate?ipid=desktopnav9-12) - [Obituaries](https://www.legacy.com/obituaries/sfgate?ipid=desktopnav9-12) - [Place an Obituary](https://ezads.hearst.com/obits/sfchronicle/index.html) [Best Of](https://www.sfgate.com/best/) [Shopping](https://www.sfgate.com/shopping/) [Puzzles](https://www.sfgate.com/puzzles/) [Sponsor Content](https://www.sfgate.com/sponsoredarticles/lifestyle/) - [StoryStudio](https://storystudio.sfgate.com/) - [Paid Press Releases](https://www.sfgate.com/business/press-releases/) - [Senior Living](https://www.sfgate.com/senior-living/) - [Sponsor Content: Business](https://www.sfgate.com/sponsoredarticles/business/) [SF Gate Logo](https://www.sfgate.com/) [CA MINI CROSSWORD](https://www.sfgate.com/california-mini-crossword-puzzle-puzzmo/?utm_source=masthead&utm_medium=button&utm_campaign=campaignname&utm_term=camini) We handpick every product we feature. We may be compensated or earn commission from the links on this page. [Shopping](https://www.sfgate.com/shopping/) # PCR vs. antigen testing: what’s the difference, and what should you buy? ## We spoke to experts to get real answers. By [Krystin Arneson](https://www.sfgate.com/author/krystin-arneson/), Freelance Writer Updated Jan 11, 2022 8:34 a.m. ![Saliva At-Home Collection Kit]() [Saliva At-Home Collection Kit](https://www.walmart.com/ip/DxTerity-SARS-CoV-2-RT-PCR-CE-Test-COVID-19-Saliva-At-Home-Collection-Kit/518633039?selected=true&irgwc=1&sourceid=imp_SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&veh=aff&wmlspartner=imp_10078&clickid=SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&sharedid=sfgate.com&affiliates_ad_id=612734&campaign_id=9383) DxTerity Two years into the pandemic, we’re getting some solid testing options finally available on a widespread basis — never mind that shortage of at-home rapid antigen tests (RATs) that happened over the duration between Christmas and New Year’s. But PCR tests and RATs remain on the pricey side, so you don’t want to spend your money on the wrong kind of test for the wrong reasons. ![](https://cdn-channels-pixel.ex.co/events/0012000001fxZm9AAE?integrationType=DEFAULT&template=design%2Farticle%2Fplatypus_two_column.tpl) “PCR (polymerase chain reaction) and antigen tests — both of which typically use nasal swabs to collect samples — differ in detection methods, processing, and turnaround times,” says Dr. Ariella Morrow from Sameday Health, a personalized healthcare provider with nationwide covid-testing clinic and services. : We’ve spoken to her and other medical experts about the differences between a PCR and RAT—as well as what situations you should use either kind of test for. ## What is the difference between a PCR and an antigen test? Each test uses a different process to detect the presence of Covid-19 in your body, with PCR tests taking a super-thorough look — if you have Covid, there’s a greater chance you’ll test positive with a PCR test than with a rapid antigen test, says Erica Susky, an infection control practitioner in hospital epidemiology, making them the best accessible way to tell if you have COVID or not. [PCR CE Test - COVID-19 Saliva At-Home Collection Kit](https://www.walmart.com/ip/DxTerity-SARS-CoV-2-RT-PCR-CE-Test-COVID-19-Saliva-At-Home-Collection-Kit/518633039?selected=true&irgwc=1&sourceid=imp_SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&veh=aff&wmlspartner=imp_10078&clickid=SM-1h1yRExyIWLPUVSRa73dbUkG3WIy5py3gTI0&sharedid=sfgate.com&affiliates_ad_id=612734&campaign_id=9383) [![PCR CE Test - COVID-19 Saliva At-Home Collection Kit]()](https://www.walmart.com/ip/518633039?selected=true) DxTerity [PCR CE Test - COVID-19 Saliva At-Home Collection Kit](https://www.walmart.com/ip/518633039?selected=true) [\$95.00 at walmart.com](https://www.walmart.com/ip/518633039?selected=true) “PCRs, a molecular test, look for the virus’ genetic material within the specimens sample, which is then processed in a lab (often resulting in a longer turnaround time),” says Morrow. “These are the most accurate tests available due to their high sensitivity, and thus, the most widely used form of covid test by the medical community. Meanwhile, antigen tests search for a piece of the virus’ protein in the sample, which can then be analyzed by a healthcare professional in real-time or at home.” [On/Go at-Home COVID-19 Rapid Antigen Self-Test](https://www.amazon.com/dp/B09FP6HWCV?ots=1&slotNum=4&imprToken=02bf22e3-a10f-acf9-b2a&tag=hearstnp-sfg-20&th=1&ascsubtag=wcm~16765004~1775691525~inl~~~~~~~B09FP6HWCV) [![at-Home COVID-19 Rapid Antigen Test]()](https://www.amazon.com/dp/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV) ON/GO [at-Home COVID-19 Rapid Antigen Test](https://www.amazon.com/dp/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV) [\$20.00 at amazon.com](https://www.amazon.com/dp/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV) Rapid antigen tests (RAT) are easier to perform because anyone can do one at home and it’s faster obtain results, says Susky. They usually take about 15 to 30 minutes for results. But there is a downside. “Although antigen tests typically provide results in under fifteen minutes," says Marrow, "they are more likely to yield false-negative results due to lesser sensitivity, especially for those that are asymptomatic.” While most people perform their own antigen tests, PCR tests are almost always administered by someone else, with samples sent to a lab for detection and analysis. “This test takes more time as it is required to be done by trained laboratory professionals,” says Susky. “Wait times can be as much as 72 hours for PCR results." ## What’s the science behind PCR and antigen tests? “PCR (or polymerase chain reaction) amplifies targeted regions of a genome,” says Erica Susky, an infection control practitioner in hospital epidemiology. “In the case of SARS-CoV-2, as the viral genome is made of RNA, there are pieces of RNA primer made in the laboratory designed to bind to areas of the SARS-CoV-2 sequence with the intention of amplifying them. The chain reaction entails temperature cycling that allow the targeted pieces of SARS-CoV-2 to be amplified so they will then be easily detected, usually with fluorescent dyes.” Since this involves amplification of parts of the SARS-CoV-2 virus, “RATs work by binding antigens to antibodies,” says Susky. “Antibodies are made by the immune system and function by binding select targets. One gets a nasal or throat specimen and puts it in a liquid buffer”— i.e. you swab your nose and then swirl it around some liquid that comes with the test kit. “The buffer is flooded onto the RAT slide,” she says. “The RAT slide contains SARS-CoV-2 antigens bound to a color marker.” If you have Covid, then the antibodies from the virus bind to the color-marked antigen in the test and you’ll see a colored band. ## PCR vs. antigen: Which one is more accurate? PCR tests are ultimately the more accurate way to tell if you have COVID-19, but antigen tests are a great first line of defense if you think you have symptoms. It's best to use PCR tests, rather than antigen tests, before higher-risk situations for you and others or when legally required, like before a flight. Susky says PCR testing “is much more sensitive than antigen testing. What this means is that with someone who has COVID-19, there is a greater chance that they will test positive by PCR than with the antigen test, or there are fewer chances of false negative results.” On the other hand, “rapid antigen tests are not as sensitive as PCR — there’s a higher chance of testing negative when one may in fact have COVID-19, but they are quite specific,” Susky says. “Something with a good specificity means that a positive result has a high probability of the presence of disease. Therefore, if one tests positive by RAT it is safe to say they have COVID-19 and should isolate at home.” ## Where can you buy antigen and PCR tests? Because PCR tests require the use of a lab, the easiest way to get a PCR test is to book it with a test provider — just be prepared to fork out some money for it. Antigen tests are now widely available and come in at [less than \$18 for two](https://www.amazon.com/iHealth-COVID-19-Authorized-Non-invasive-Discomfort/dp/B09KZ6TBNY/ref=sr_1_5?crid=37ZR24MZK5OHW&keywords=PCR+covid+test&qid=1640728076&sprefix=pcr+covid+test%2Caps%2C110&sr=8-5&tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~inl~~~~~~~B09KZ6TBNY) on sites like Amazon, which isn’t cheap but a lot better than spreading COVID-19. Jan 10, 2022 \\|Updated Jan 11, 2022 8:34 a.m. [Krystin Arneson](https://www.sfgate.com/author/krystin-arneson/) Freelance Writer Krystin Arneson is a freelance writer and editor based in Europe (and frequently elsewhere). When not covering shopping, she's writing about travel, wine, or culture. [Best Of](https://www.sfgate.com/best) Best Of [Top-rated appliance repair companies in the Bay Area](https://www.sfgate.com/best/map/top-rated-appliance-repair-companies-bay-area/) [Call these pros with your dishwasher's on the fritz.](https://www.sfgate.com/best/map/top-rated-appliance-repair-companies-bay-area/) [![Top-rated appliance repair companies in the Bay Area]()](https://www.sfgate.com/best/map/top-rated-appliance-repair-companies-bay-area/) Best Of [Why homeowners use USA Bath for bathroom upgrades](https://www.sfgate.com/best/map/best-bathroom-remodeling-companies-sacramento/#usabath) [If your bathroom feels outdated, USA Bath specializes in remodels. 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Readable Markdown	![Saliva At-Home Collection Kit]() DxTerity Two years into the pandemic, we’re getting some solid testing options finally available on a widespread basis — never mind that shortage of at-home rapid antigen tests (RATs) that happened over the duration between Christmas and New Year’s. But PCR tests and RATs remain on the pricey side, so you don’t want to spend your money on the wrong kind of test for the wrong reasons. “PCR (polymerase chain reaction) and antigen tests — both of which typically use nasal swabs to collect samples — differ in detection methods, processing, and turnaround times,” says Dr. Ariella Morrow from Sameday Health, a personalized healthcare provider with nationwide covid-testing clinic and services. : We’ve spoken to her and other medical experts about the differences between a PCR and RAT—as well as what situations you should use either kind of test for. What is the difference between a PCR and an antigen test? Each test uses a different process to detect the presence of Covid-19 in your body, with PCR tests taking a super-thorough look — if you have Covid, there’s a greater chance you’ll test positive with a PCR test than with a rapid antigen test, says Erica Susky, an infection control practitioner in hospital epidemiology, making them the best accessible way to tell if you have COVID or not. [![PCR CE Test - COVID-19 Saliva At-Home Collection Kit]()](https://www.walmart.com/ip/518633039?selected=true) “PCRs, a molecular test, look for the virus’ genetic material within the specimens sample, which is then processed in a lab (often resulting in a longer turnaround time),” says Morrow. “These are the most accurate tests available due to their high sensitivity, and thus, the most widely used form of covid test by the medical community. Meanwhile, antigen tests search for a piece of the virus’ protein in the sample, which can then be analyzed by a healthcare professional in real-time or at home.” [![at-Home COVID-19 Rapid Antigen Test]()](https://www.amazon.com/dp/B09FP6HWCV?tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~cch~~~~~~~B09FP6HWCV) Rapid antigen tests (RAT) are easier to perform because anyone can do one at home and it’s faster obtain results, says Susky. They usually take about 15 to 30 minutes for results. But there is a downside. “Although antigen tests typically provide results in under fifteen minutes," says Marrow, "they are more likely to yield false-negative results due to lesser sensitivity, especially for those that are asymptomatic.” While most people perform their own antigen tests, PCR tests are almost always administered by someone else, with samples sent to a lab for detection and analysis. “This test takes more time as it is required to be done by trained laboratory professionals,” says Susky. “Wait times can be as much as 72 hours for PCR results." What’s the science behind PCR and antigen tests? “PCR (or polymerase chain reaction) amplifies targeted regions of a genome,” says Erica Susky, an infection control practitioner in hospital epidemiology. “In the case of SARS-CoV-2, as the viral genome is made of RNA, there are pieces of RNA primer made in the laboratory designed to bind to areas of the SARS-CoV-2 sequence with the intention of amplifying them. The chain reaction entails temperature cycling that allow the targeted pieces of SARS-CoV-2 to be amplified so they will then be easily detected, usually with fluorescent dyes.” Since this involves amplification of parts of the SARS-CoV-2 virus, “RATs work by binding antigens to antibodies,” says Susky. “Antibodies are made by the immune system and function by binding select targets. One gets a nasal or throat specimen and puts it in a liquid buffer”— i.e. you swab your nose and then swirl it around some liquid that comes with the test kit. “The buffer is flooded onto the RAT slide,” she says. “The RAT slide contains SARS-CoV-2 antigens bound to a color marker.” If you have Covid, then the antibodies from the virus bind to the color-marked antigen in the test and you’ll see a colored band. PCR vs. antigen: Which one is more accurate? PCR tests are ultimately the more accurate way to tell if you have COVID-19, but antigen tests are a great first line of defense if you think you have symptoms. It's best to use PCR tests, rather than antigen tests, before higher-risk situations for you and others or when legally required, like before a flight. Susky says PCR testing “is much more sensitive than antigen testing. What this means is that with someone who has COVID-19, there is a greater chance that they will test positive by PCR than with the antigen test, or there are fewer chances of false negative results.” On the other hand, “rapid antigen tests are not as sensitive as PCR — there’s a higher chance of testing negative when one may in fact have COVID-19, but they are quite specific,” Susky says. “Something with a good specificity means that a positive result has a high probability of the presence of disease. Therefore, if one tests positive by RAT it is safe to say they have COVID-19 and should isolate at home.” Where can you buy antigen and PCR tests? Because PCR tests require the use of a lab, the easiest way to get a PCR test is to book it with a test provider — just be prepared to fork out some money for it. Antigen tests are now widely available and come in at [less than \$18 for two](https://www.amazon.com/iHealth-COVID-19-Authorized-Non-invasive-Discomfort/dp/B09KZ6TBNY/ref=sr_1_5?crid=37ZR24MZK5OHW&keywords=PCR+covid+test&qid=1640728076&sprefix=pcr+covid+test%2Caps%2C110&sr=8-5&tag=hearstnp-sfg-20&ascsubtag=wcm~16765004~1775691525~inl~~~~~~~B09KZ6TBNY) on sites like Amazon, which isn’t cheap but a lot better than spreading COVID-19. Jan 10, 2022 \\|Updated Jan 11, 2022 8:34 a.m. Freelance Writer Krystin Arneson is a freelance writer and editor based in Europe (and frequently elsewhere). When not covering shopping, she's writing about travel, wine, or culture.
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