🕷️ Crawler Inspector

URL Lookup

Direct Parameter Lookup

Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 143 (from laksa027)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa143.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://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing\')), getAhrefsUnparsedNoserviceFromURL(\'https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing","crawl_time":1775902306,"first_indexed_time":1607368241,"http_code":200,"src_unparsed":"org,clevelandclinic!my,\/health\/diagnostics\/21462-covid-19-and-pcr-testing s443","src_root_hash":"9889140825964526943","history_drop_reason":null,"meta_title":"PCR Test: What It Is, How It Works & Results","meta_descriptions":["A PCR (polymerase chain reaction) test is a way for healthcare providers to diagnose illnesses or look for gene changes using small amounts of genetic material."],"attrs_boilerpipe_text":"What kind of tests or procedures use PCR?\nMany types of tests that use body fluids to look for genetic changes or infectious diseases use PCR. The type of test or procedure you need in order to get a sample depends on what you’re being tested for. Tests and procedures that use PCR include:\nBlood tests\n. Providers use a sample of blood to look for gene changes and some infectious diseases.\nNasopharyngeal swab\n.\nA lab can use a sample of mucus from your nose to look for common infections, like influenza (\nthe flu\n), COVID or respiratory syncytial virus (\nRSV\n).\nPreimplantation genetic diagnosis\/PGD or preimplantation genetic screening\/PGS\n. For preimplantation testing during\nin vitro fertilization\n(IVF), a lab will test a few cells from embryos before implantation. This usually happens a few days after egg retrieval.\nAmniocentesis\n. Providers use a sample of\namniotic fluid\nfor\nprenatal testing\n.\nBiopsy\n. To diagnose genetic mutations in tumor cells (molecular testing), you’ll need a tumor or\nbone marrow biopsy\n.\nHow to prepare for this test\nMost of the time, you don’t need to prepare for a PCR test. But it depends on what you’re being tested for and the procedure you’re having. Ask your healthcare provider if there’s anything you need to do before the test.\nHow does it work?\nPCR identifies a very specific sequence of molecules that’s unique to the DNA it’s looking for (target DNA). For example, this sequence could be a specific gene change in a tumor or the genetic code of a virus or\nbacteria\n.\nThe name “polymerase chain reaction” refers to how the lab amplifies (makes more copies of) the target DNA. It uses an\nenzyme\ncalled DNA polymerase to build strings of DNA that copy the target DNA, if it’s present. The chain reaction happens when many cycles of heating and cooling a solution make more and more copies, potentially doubling the amount of target DNA each time. This means that PCR works with samples of DNA (or RNA) that are so small that they might be missed in other tests.\nOften, after PCR is complete, scientists might have to run other tests to analyze the sample — now with potentially millions of copies of the target DNA.\nOther times, the solution has labels that allow a healthcare professional to see whether the sample is positive or negative for the target DNA during the PCR amplification. In testing for infectious diseases, like viruses, this allows for quicker results, since you don’t need any additional testing.\nTypes of PCR\nSome types of PCR require additional steps to amplify or analyze the target DNA:\nReverse-transcriptase PCR (RT-PCR).\nScientists use RT-PCR when the genetic information they want to copy is in the form of RNA rather than DNA. There are extra steps that make the RNA into complementary DNA (cDNA), so that a PCR can be performed. (Without this step, PCR can only be performed on DNA.)\nReal-time PCR\/quantitative PCR (Q-PCR).\nIn real-time PCR, scientists add fluorescent labels to the DNA that mark the target DNA. This allows them to see whether the target DNA is in the sample without an additional test. Confusingly, some people also refer to this as “RT-PCR,” and it can also be combined with reverse-transcriptase PCR (real-time RT-PCR).\nHealthcare professionals use real-time RT-PCR for nasal swab tests for COVID-19 and the flu. SARS-CoV-2 (COVID-19) and influenza viruses are RNA viruses.","attrs_markdown":"![](https:\/\/zdbb.net\/l\/Dnl1wmWs8xCCpvWNCt9Egf\/?w=16&q=75)\n\nLocations:\n\n[Abu Dhabi](https:\/\/www.clevelandclinicabudhabi.ae\/en)\\|[Canada](https:\/\/my.clevelandclinic.org\/canada)\\|[Florida](https:\/\/my.clevelandclinic.org\/florida)\\|[London](https:\/\/clevelandcliniclondon.uk\/)\\|[Nevada](https:\/\/my.clevelandclinic.org\/locations\/nevada)\\|[Ohio](https:\/\/my.clevelandclinic.org\/)\\|\n\n![Gray gradient](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/gray-gradient-left-16.59910877.svg?w=32&q=75)![Gray gradient](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/gray-gradient-right-32.dd7ce4e5.svg?w=64&q=75)\n\n[855\\.733.3712](tel:8557333712)\\|[MyChart](https:\/\/my.clevelandclinic.org\/online-services\/mychart)\\|[Need Help?](https:\/\/my.clevelandclinic.org\/help)\\|[Careers](https:\/\/jobs.clevelandclinic.org\/)\\|[Donate Now](https:\/\/give.ccf.org\/give\/187824#!\/donation\/checkout)\\|\n\n![Gray gradient](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/gray-gradient-left-16.59910877.svg?w=32&q=75)![Gray gradient](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/gray-gradient-right-32.dd7ce4e5.svg?w=64&q=75)\n\n[![Cleveland Clinic logo](https:\/\/assets.clevelandclinic.org\/transform\/1bc1ff31-3cbc-4976-9ddf-9bc85e0877eb\/Cleveland-Clinic-Logo-Web?w=3840&q=75)](https:\/\/my.clevelandclinic.org\/)\n\n[Find a Provider](https:\/\/my.clevelandclinic.org\/providers)[Locations and Directions](https:\/\/my.clevelandclinic.org\/locations)[Services](https:\/\/my.clevelandclinic.org\/services)[Patients and Visitors](https:\/\/my.clevelandclinic.org\/patients)[Health Library](https:\/\/my.clevelandclinic.org\/health)\n\n- [Find a Provider](https:\/\/my.clevelandclinic.org\/providers)\n- [Locations and Directions](https:\/\/my.clevelandclinic.org\/locations)\n- [Services](https:\/\/my.clevelandclinic.org\/services)\n- [Patients and Visitors](https:\/\/my.clevelandclinic.org\/patients)\n- [Health Library](https:\/\/my.clevelandclinic.org\/health)\n\n[![Search](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/LondonGreenSearchIcon.6d7e718f.svg?w=64&q=75)](https:\/\/my.clevelandclinic.org\/search)\n\nMenu\n\n[![Search](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/LondonGreenSearchIcon.6d7e718f.svg?w=64&q=75)](https:\/\/my.clevelandclinic.org\/search)[Appointments](https:\/\/my.clevelandclinic.org\/patients\/information\/access)\n\n[Home](https:\/\/my.clevelandclinic.org\/)\/\n\n[Health Library](https:\/\/my.clevelandclinic.org\/health)\/\n\n[Diagnostics & Testing](https:\/\/my.clevelandclinic.org\/health\/diagnostics)\/\n\nPCR Test\n\nAdvertisement\n\nAdvertisement\n# PCR Test\nMedically Reviewed.\n\nLast updated on 01\/21\/2025.\n\nA PCR (polymerase chain reaction) test is a lab technique that amplifies (creates more copies) of genetic material (DNA). Healthcare providers can use PCR to test for infectious diseases, to look for genetic changes in tumors or to diagnose genetic diseases. Nasal swab tests for COVID-19 and influenza are a common example of a PCR test.\n\nAdvertisement\n\nCleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. [Policy](https:\/\/health.clevelandclinic.org\/advertising)\n\nCare at Cleveland Clinic\n\n[Get Cold, Flu & COVID-19 Care](https:\/\/my.clevelandclinic.org\/services\/cold-flu-covid-19-care)\n\n[Find a Walk-in Location Near You](https:\/\/my.clevelandclinic.org\/services\/cold-flu-covid-19-care#locations-panel)\n\nContents\n\n[What is a PCR test?](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing#what-is-a-pcr-test)[Test Details](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing#test-details)[Results and Follow-Up](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing#results-and-follow-up)\n\nContents\n\n[What is a PCR test?](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing#what-is-a-pcr-test)[Test Details](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing#test-details)[Results and Follow-Up](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/21462-covid-19-and-pcr-testing#results-and-follow-up)\n\n## What is a PCR test?\nA PCR (polymerase chain reaction) test is a way to look for genetic material ([DNA](https:\/\/my.clevelandclinic.org\/health\/body\/dna) or RNA). After taking a body fluid sample (like [blood](https:\/\/my.clevelandclinic.org\/health\/body\/24836-blood)) or a swab from a body site (like deep in your nose), scientists use PCR to make many copies of DNA (amplification) that was in the original sample. By amplifying with PCR, scientists can better analyze the DNA or RNA that was in the original sample.\n\nAdvertisement\n\nCleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. [Policy](https:\/\/health.clevelandclinic.org\/advertising)\n\nThere are many PCR tests. Each is different and is designed for a certain purpose. For example, some PCR tests can determine if a specific [virus](https:\/\/my.clevelandclinic.org\/health\/body\/24861-virus) is present in the sample, which might be making you sick. Other PCR tests can determine if certain genes in your body might have important changes.\n\nMost of us know the term “PCR test” because of testing for [COVID-19](https:\/\/my.clevelandclinic.org\/health\/diseases\/21214-coronavirus-covid-19). But it’s been used in medicine for a long time and has many other uses. Any test that uses a polymerase chain reaction technique is a PCR test. PCR is a type of nucleic acid amplification test (NAAT).\n\n### What is a COVID-19 PCR test?\nHealthcare providers can use a PCR test to determine whether you have a COVID infection. They use a swab to get a sample of [mucus](https:\/\/my.clevelandclinic.org\/health\/body\/mucus) or secretions from deep in your nose. PCR is then used to determine if genetic material (RNA) of SARS-CoV-2 (the virus that causes COVID) in your sample.\n\n### What can PCR detect?\nHealthcare professionals perform PCR tests for many reasons. PCR can diagnose or detect:\n\n- [Infectious diseases](https:\/\/my.clevelandclinic.org\/health\/diseases\/17724-infectious-diseases) (viruses, [bacteria](https:\/\/my.clevelandclinic.org\/health\/articles\/24494-bacteria), fungi and [parasites](https:\/\/my.clevelandclinic.org\/health\/diseases\/24911-parasites))\n- Genetic diseases, like [cystic fibrosis](https:\/\/my.clevelandclinic.org\/health\/diseases\/9358-cystic-fibrosis), Huntington’s disease, [fragile X syndrome](https:\/\/my.clevelandclinic.org\/health\/diseases\/5476-fragile-x-syndrome) and others\n- Types of cancer, like [lymphoma](https:\/\/my.clevelandclinic.org\/health\/diseases\/22225-lymphoma)\n- Gene changes (variations) in cancer that can be targeted with specific medications.\n- Gene changes that can put you at higher risk for certain diseases (like [genetic testing for cancer risk](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/23972-genetic-testing-cancer-risk))\n- Gene changes in [prenatal testing](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/24136-pregnancy-genetic-testing)\n\nAdvertisement\n\nForensic labs can also use PCR to create detectable amounts of DNA found at crime scenes.\n\n## Test Details\n### What kind of tests or procedures use PCR?\nMany types of tests that use body fluids to look for genetic changes or infectious diseases use PCR. The type of test or procedure you need in order to get a sample depends on what you’re being tested for. Tests and procedures that use PCR include:\n\n- [**Blood tests**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/24508-blood-tests). Providers use a sample of blood to look for gene changes and some infectious diseases.\n- [**Nasopharyngeal swab**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/22878-nasopharyngeal-swab).A lab can use a sample of mucus from your nose to look for common infections, like influenza ([the flu](https:\/\/my.clevelandclinic.org\/health\/diseases\/4335-influenza-flu)), COVID or respiratory syncytial virus ([RSV](https:\/\/my.clevelandclinic.org\/health\/diseases\/rsv-respiratory-syncytial-virus)).\n- **Preimplantation genetic diagnosis\/PGD or preimplantation genetic screening\/PGS**. For preimplantation testing during [in vitro fertilization](https:\/\/my.clevelandclinic.org\/health\/treatments\/22457-ivf) (IVF), a lab will test a few cells from embryos before implantation. This usually happens a few days after egg retrieval.\n- [**Amniocentesis**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/4206-genetic-amniocentesis). Providers use a sample of [amniotic fluid](https:\/\/my.clevelandclinic.org\/health\/body\/23310-amniotic-fluid) for [prenatal testing](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/24136-pregnancy-genetic-testing).\n- [**Biopsy**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/15458-biopsy-overview). To diagnose genetic mutations in tumor cells (molecular testing), you’ll need a tumor or [bone marrow biopsy](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/17735-bone-marrow-biopsy).\n#### How to prepare for this test\nMost of the time, you don’t need to prepare for a PCR test. But it depends on what you’re being tested for and the procedure you’re having. Ask your healthcare provider if there’s anything you need to do before the test.\n\n### How does it work?\nPCR identifies a very specific sequence of molecules that’s unique to the DNA it’s looking for (target DNA). For example, this sequence could be a specific gene change in a tumor or the genetic code of a virus or [bacteria](https:\/\/my.clevelandclinic.org\/health\/articles\/24494-bacteria).\n\nThe name “polymerase chain reaction” refers to how the lab amplifies (makes more copies of) the target DNA. It uses an [enzyme](https:\/\/my.clevelandclinic.org\/health\/articles\/21532-enzymes) called DNA polymerase to build strings of DNA that copy the target DNA, if it’s present. The chain reaction happens when many cycles of heating and cooling a solution make more and more copies, potentially doubling the amount of target DNA each time. This means that PCR works with samples of DNA (or RNA) that are so small that they might be missed in other tests.\n\nOften, after PCR is complete, scientists might have to run other tests to analyze the sample — now with potentially millions of copies of the target DNA.\n\nOther times, the solution has labels that allow a healthcare professional to see whether the sample is positive or negative for the target DNA during the PCR amplification. In testing for infectious diseases, like viruses, this allows for quicker results, since you don’t need any additional testing.\n\n#### Types of PCR\nSome types of PCR require additional steps to amplify or analyze the target DNA:\n\nAdvertisement\n\n- **Reverse-transcriptase PCR (RT-PCR).** Scientists use RT-PCR when the genetic information they want to copy is in the form of RNA rather than DNA. There are extra steps that make the RNA into complementary DNA (cDNA), so that a PCR can be performed. (Without this step, PCR can only be performed on DNA.)\n- **Real-time PCR\/quantitative PCR (Q-PCR).** In real-time PCR, scientists add fluorescent labels to the DNA that mark the target DNA. This allows them to see whether the target DNA is in the sample without an additional test. Confusingly, some people also refer to this as “RT-PCR,” and it can also be combined with reverse-transcriptase PCR (real-time RT-PCR).\n\nHealthcare professionals use real-time RT-PCR for nasal swab tests for COVID-19 and the flu. SARS-CoV-2 (COVID-19) and influenza viruses are RNA viruses.\n\nCare at Cleveland Clinic\n\n[Get Cold, Flu & COVID-19 Care](https:\/\/my.clevelandclinic.org\/services\/cold-flu-covid-19-care)\n\n[Find a Walk-in Location Near You](https:\/\/my.clevelandclinic.org\/services\/cold-flu-covid-19-care#locations-panel)\n\n## Results and Follow-Up\n### What do the results of a PCR test mean?\nPCR tests might use different language in your results, depending on what you’re being tested for. For example, if your results say “detected” or “present,” it generally means you have the gene change or infection that the test was looking for.\n\nIf the results say “not detected,” it means the test didn’t find the target DNA or RNA. In the case of an infection, this can sometimes mean that you were tested too early in an infection. You could still have an infection, but there weren’t enough viruses, bacteria or other diseases to be detectable, even with PCR.\n\nAdvertisement\n\n#### What do COVID PCR test results mean?\nA positive COVID PCR test result — if you see the word “detected” on your result — means that it’s likely that you have COVID or that you’ve recently recovered from it.\n\nA negative (“not detected”) COVID PCR test result means you probably didn’t have COVID at the time of your nasal swab. But sometimes, PCR tests can be negative very early on in an infection, especially if you don’t have symptoms yet.\n\n#### When should I know the results of a PCR test?\nThe results of nasal swab tests for common viruses like influenza and COVID usually take about a day to come back. The results of genetic testing through blood tests, biopsies and other procedures can take at least a week or longer.\n\n### When should I call my doctor?\nContact your healthcare provider if you have any questions about a PCR test or its results.\n### A note from Cleveland Clinic\nThe term “PCR test” suddenly became a part of everyday conversations with the COVID-19 pandemic back in 2020. But healthcare professionals have used PCR techniques for decades. By copying and detecting tiny amounts of DNA, PCR can help diagnose a variety of health conditions.\n\nBut just because it’s routine for medical professionals doesn’t mean a test is routine for you. Fortunately, it only takes a small sample from your body to work, and your part is usually over in a few moments. Talk to your provider if you have any questions or concerns.\n\nAdvertisement\n\n[![Cleveland Clinic logo](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/logo-ccf.1e52a22b.svg?w=3840&q=75)](https:\/\/my.clevelandclinic.org\/)[![Cleveland Clinic icon](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/CCFLogo.000428c6.svg?w=3840&q=75)](https:\/\/my.clevelandclinic.org\/)\n\n[![Health Essentials logo](https:\/\/my.clevelandclinic.org\/_next\/static\/media\/HealthEssentials.b811bb06.svg?w=3840&q=75)](https:\/\/health.clevelandclinic.org\/)\n\n![Subscription icon](https:\/\/assets.clevelandclinic.org\/transform\/482db8cd-aa1e-45b5-a2a4-cf6aa5e5d2d4\/Health-Essentials?w=256&q=75)\n\n## Better health starts here\nSign up for our Health Essentials emails for expert guidance on nutrition, fitness, sleep, skin care and more.\n\n[Example email](https:\/\/assets.clevelandclinic.org\/transform\/2ff943a2-abb1-4a1c-8ede-f8848703e789\/HealthEssentials-SampleEmail-2026)[Sign up](https:\/\/my.clevelandclinic.org\/health-essentials-sign-up)\n\n[Sign up](https:\/\/my.clevelandclinic.org\/health-essentials-sign-up)[Example email](https:\/\/assets.clevelandclinic.org\/transform\/2ff943a2-abb1-4a1c-8ede-f8848703e789\/HealthEssentials-SampleEmail-2026)\n\n### Experts You Can Trust\nMedically Reviewed.\n\nLast updated on 01\/21\/2025.\n\nLearn more about the [Health Library](https:\/\/my.clevelandclinic.org\/health\/about) and our [editorial process](https:\/\/my.clevelandclinic.org\/about\/website\/editorial-policy).\n\n### References\nCleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.\n#### View Sources\n\n### Experts You Can Trust\nMedically Reviewed.\n\nLast updated on 01\/21\/2025.\n\n### References\nCleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.\n\n- National Library of Medicine (U.S.). PCR Tests *(https:\/\/medlineplus.gov\/lab-tests\/pcr-tests\/)*. Updated 9\/19\/2024. Accessed 1\/16\/2025.\n- Waters DL, Shapter FM. The polymerase chain reaction (PCR): general methods *(https:\/\/pubmed.ncbi.nlm.nih.gov\/24243196\/)*. *Methods Mol Biol.* 2014;1099:65-75. Accessed 1\/16\/2025.\n- Weil P. Molecular Genetics, Recombinant DNA, & Genomic Technology. In: Kennelly PJ, Botham KM, McGuinness OP, Rodwell VW, Weil P, eds. *Harper’s Illustrated Biochemistry.* 32nd ed. McGraw Hill Education; 2023.\n\n### Care at Cleveland Clinic\nCold, flu or COVID-19? Cleveland Clinic will help you figure out what to do next.\n\n![Doctor listens to patient's chest with stethoscope during a medical office exam.](https:\/\/my.clevelandclinic.org\/-\/scassets\/images\/org\/care-pages\/primary-care\/cold-flu-covid-feature.jpg?w=640&q=75)\n\n[Get Cold, Flu & COVID-19 Care](https:\/\/my.clevelandclinic.org\/services\/cold-flu-covid-19-care)\n\n[Find a Walk-in Location Near You](https:\/\/my.clevelandclinic.org\/services\/cold-flu-covid-19-care#locations-panel)\n\nAdvertisement\n\nAdvertisement\n\nAd\n\n[Lab Appointments & Locations](https:\/\/my.clevelandclinic.org\/departments\/pathology\/appointments-locations?fR[searchCollections][0]=12)\n\n[Find a ProviderNeed a primary care doctor or a specialist? 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All Rights Reserved.","attrs_readable_markdown":"### What kind of tests or procedures use PCR?\nMany types of tests that use body fluids to look for genetic changes or infectious diseases use PCR. The type of test or procedure you need in order to get a sample depends on what you’re being tested for. Tests and procedures that use PCR include:\n\n- [**Blood tests**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/24508-blood-tests). Providers use a sample of blood to look for gene changes and some infectious diseases.\n- [**Nasopharyngeal swab**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/22878-nasopharyngeal-swab).A lab can use a sample of mucus from your nose to look for common infections, like influenza ([the flu](https:\/\/my.clevelandclinic.org\/health\/diseases\/4335-influenza-flu)), COVID or respiratory syncytial virus ([RSV](https:\/\/my.clevelandclinic.org\/health\/diseases\/rsv-respiratory-syncytial-virus)).\n- **Preimplantation genetic diagnosis\/PGD or preimplantation genetic screening\/PGS**. For preimplantation testing during [in vitro fertilization](https:\/\/my.clevelandclinic.org\/health\/treatments\/22457-ivf) (IVF), a lab will test a few cells from embryos before implantation. This usually happens a few days after egg retrieval.\n- [**Amniocentesis**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/4206-genetic-amniocentesis). Providers use a sample of [amniotic fluid](https:\/\/my.clevelandclinic.org\/health\/body\/23310-amniotic-fluid) for [prenatal testing](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/24136-pregnancy-genetic-testing).\n- [**Biopsy**](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/15458-biopsy-overview). To diagnose genetic mutations in tumor cells (molecular testing), you’ll need a tumor or [bone marrow biopsy](https:\/\/my.clevelandclinic.org\/health\/diagnostics\/17735-bone-marrow-biopsy).\n#### How to prepare for this test\nMost of the time, you don’t need to prepare for a PCR test. But it depends on what you’re being tested for and the procedure you’re having. Ask your healthcare provider if there’s anything you need to do before the test.\n\n### How does it work?\nPCR identifies a very specific sequence of molecules that’s unique to the DNA it’s looking for (target DNA). For example, this sequence could be a specific gene change in a tumor or the genetic code of a virus or [bacteria](https:\/\/my.clevelandclinic.org\/health\/articles\/24494-bacteria).\n\nThe name “polymerase chain reaction” refers to how the lab amplifies (makes more copies of) the target DNA. It uses an [enzyme](https:\/\/my.clevelandclinic.org\/health\/articles\/21532-enzymes) called DNA polymerase to build strings of DNA that copy the target DNA, if it’s present. The chain reaction happens when many cycles of heating and cooling a solution make more and more copies, potentially doubling the amount of target DNA each time. This means that PCR works with samples of DNA (or RNA) that are so small that they might be missed in other tests.\n\nOften, after PCR is complete, scientists might have to run other tests to analyze the sample — now with potentially millions of copies of the target DNA.\n\nOther times, the solution has labels that allow a healthcare professional to see whether the sample is positive or negative for the target DNA during the PCR amplification. In testing for infectious diseases, like viruses, this allows for quicker results, since you don’t need any additional testing.\n\n#### Types of PCR\nSome types of PCR require additional steps to amplify or analyze the target DNA:\n\n- **Reverse-transcriptase PCR (RT-PCR).** Scientists use RT-PCR when the genetic information they want to copy is in the form of RNA rather than DNA. There are extra steps that make the RNA into complementary DNA (cDNA), so that a PCR can be performed. (Without this step, PCR can only be performed on DNA.)\n- **Real-time PCR\/quantitative PCR (Q-PCR).** In real-time PCR, scientists add fluorescent labels to the DNA that mark the target DNA. This allows them to see whether the target DNA is in the sample without an additional test. Confusingly, some people also refer to this as “RT-PCR,” and it can also be combined with reverse-transcriptase PCR (real-time RT-PCR).\n\nHealthcare professionals use real-time RT-PCR for nasal swab tests for COVID-19 and the flu. SARS-CoV-2 (COVID-19) and influenza viruses are RNA viruses.","meta_canonical":null}

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Meta Title	PCR Test: What It Is, How It Works & Results
Meta Description	A PCR (polymerase chain reaction) test is a way for healthcare providers to diagnose illnesses or look for gene changes using small amounts of genetic material.
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Boilerpipe Text	What kind of tests or procedures use PCR? Many types of tests that use body fluids to look for genetic changes or infectious diseases use PCR. The type of test or procedure you need in order to get a sample depends on what you’re being tested for. Tests and procedures that use PCR include: Blood tests . Providers use a sample of blood to look for gene changes and some infectious diseases. Nasopharyngeal swab . A lab can use a sample of mucus from your nose to look for common infections, like influenza ( the flu ), COVID or respiratory syncytial virus ( RSV ). Preimplantation genetic diagnosis/PGD or preimplantation genetic screening/PGS . For preimplantation testing during in vitro fertilization (IVF), a lab will test a few cells from embryos before implantation. This usually happens a few days after egg retrieval. Amniocentesis . Providers use a sample of amniotic fluid for prenatal testing . Biopsy . To diagnose genetic mutations in tumor cells (molecular testing), you’ll need a tumor or bone marrow biopsy . How to prepare for this test Most of the time, you don’t need to prepare for a PCR test. But it depends on what you’re being tested for and the procedure you’re having. Ask your healthcare provider if there’s anything you need to do before the test. How does it work? PCR identifies a very specific sequence of molecules that’s unique to the DNA it’s looking for (target DNA). For example, this sequence could be a specific gene change in a tumor or the genetic code of a virus or bacteria . The name “polymerase chain reaction” refers to how the lab amplifies (makes more copies of) the target DNA. It uses an enzyme called DNA polymerase to build strings of DNA that copy the target DNA, if it’s present. The chain reaction happens when many cycles of heating and cooling a solution make more and more copies, potentially doubling the amount of target DNA each time. This means that PCR works with samples of DNA (or RNA) that are so small that they might be missed in other tests. Often, after PCR is complete, scientists might have to run other tests to analyze the sample — now with potentially millions of copies of the target DNA. Other times, the solution has labels that allow a healthcare professional to see whether the sample is positive or negative for the target DNA during the PCR amplification. In testing for infectious diseases, like viruses, this allows for quicker results, since you don’t need any additional testing. Types of PCR Some types of PCR require additional steps to amplify or analyze the target DNA: Reverse-transcriptase PCR (RT-PCR). Scientists use RT-PCR when the genetic information they want to copy is in the form of RNA rather than DNA. There are extra steps that make the RNA into complementary DNA (cDNA), so that a PCR can be performed. (Without this step, PCR can only be performed on DNA.) Real-time PCR/quantitative PCR (Q-PCR). In real-time PCR, scientists add fluorescent labels to the DNA that mark the target DNA. This allows them to see whether the target DNA is in the sample without an additional test. Confusingly, some people also refer to this as “RT-PCR,” and it can also be combined with reverse-transcriptase PCR (real-time RT-PCR). Healthcare professionals use real-time RT-PCR for nasal swab tests for COVID-19 and the flu. SARS-CoV-2 (COVID-19) and influenza viruses are RNA viruses.
Markdown	![](https://zdbb.net/l/Dnl1wmWs8xCCpvWNCt9Egf/?w=16&q=75) Locations: [Abu Dhabi](https://www.clevelandclinicabudhabi.ae/en)\\|[Canada](https://my.clevelandclinic.org/canada)\\|[Florida](https://my.clevelandclinic.org/florida)\\|[London](https://clevelandcliniclondon.uk/)\\|[Nevada](https://my.clevelandclinic.org/locations/nevada)\\|[Ohio](https://my.clevelandclinic.org/)\\| ![Gray gradient](https://my.clevelandclinic.org/_next/static/media/gray-gradient-left-16.59910877.svg?w=32&q=75)![Gray gradient](https://my.clevelandclinic.org/_next/static/media/gray-gradient-right-32.dd7ce4e5.svg?w=64&q=75) [855\.733.3712](tel:8557333712)\\|[MyChart](https://my.clevelandclinic.org/online-services/mychart)\\|[Need Help?](https://my.clevelandclinic.org/help)\\|[Careers](https://jobs.clevelandclinic.org/)\\|[Donate Now](https://give.ccf.org/give/187824#!/donation/checkout)\\| ![Gray gradient](https://my.clevelandclinic.org/_next/static/media/gray-gradient-left-16.59910877.svg?w=32&q=75)![Gray gradient](https://my.clevelandclinic.org/_next/static/media/gray-gradient-right-32.dd7ce4e5.svg?w=64&q=75) [![Cleveland Clinic logo](https://assets.clevelandclinic.org/transform/1bc1ff31-3cbc-4976-9ddf-9bc85e0877eb/Cleveland-Clinic-Logo-Web?w=3840&q=75)](https://my.clevelandclinic.org/) [Find a Provider](https://my.clevelandclinic.org/providers)[Locations and Directions](https://my.clevelandclinic.org/locations)[Services](https://my.clevelandclinic.org/services)[Patients and Visitors](https://my.clevelandclinic.org/patients)[Health Library](https://my.clevelandclinic.org/health) - [Find a Provider](https://my.clevelandclinic.org/providers) - [Locations and Directions](https://my.clevelandclinic.org/locations) - [Services](https://my.clevelandclinic.org/services) - [Patients and Visitors](https://my.clevelandclinic.org/patients) - [Health Library](https://my.clevelandclinic.org/health) [![Search](https://my.clevelandclinic.org/_next/static/media/LondonGreenSearchIcon.6d7e718f.svg?w=64&q=75)](https://my.clevelandclinic.org/search) Menu [![Search](https://my.clevelandclinic.org/_next/static/media/LondonGreenSearchIcon.6d7e718f.svg?w=64&q=75)](https://my.clevelandclinic.org/search)[Appointments](https://my.clevelandclinic.org/patients/information/access) [Home](https://my.clevelandclinic.org/)/ [Health Library](https://my.clevelandclinic.org/health)/ [Diagnostics & Testing](https://my.clevelandclinic.org/health/diagnostics)/ PCR Test Advertisement Advertisement # PCR Test Medically Reviewed. Last updated on 01/21/2025. A PCR (polymerase chain reaction) test is a lab technique that amplifies (creates more copies) of genetic material (DNA). Healthcare providers can use PCR to test for infectious diseases, to look for genetic changes in tumors or to diagnose genetic diseases. Nasal swab tests for COVID-19 and influenza are a common example of a PCR test. Advertisement Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. [Policy](https://health.clevelandclinic.org/advertising) Care at Cleveland Clinic [Get Cold, Flu & COVID-19 Care](https://my.clevelandclinic.org/services/cold-flu-covid-19-care) [Find a Walk-in Location Near You](https://my.clevelandclinic.org/services/cold-flu-covid-19-care#locations-panel) Contents [What is a PCR test?](https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing#what-is-a-pcr-test)[Test Details](https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing#test-details)[Results and Follow-Up](https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing#results-and-follow-up) Contents [What is a PCR test?](https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing#what-is-a-pcr-test)[Test Details](https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing#test-details)[Results and Follow-Up](https://my.clevelandclinic.org/health/diagnostics/21462-covid-19-and-pcr-testing#results-and-follow-up) ## What is a PCR test? A PCR (polymerase chain reaction) test is a way to look for genetic material ([DNA](https://my.clevelandclinic.org/health/body/dna) or RNA). After taking a body fluid sample (like [blood](https://my.clevelandclinic.org/health/body/24836-blood)) or a swab from a body site (like deep in your nose), scientists use PCR to make many copies of DNA (amplification) that was in the original sample. By amplifying with PCR, scientists can better analyze the DNA or RNA that was in the original sample. Advertisement Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. [Policy](https://health.clevelandclinic.org/advertising) There are many PCR tests. Each is different and is designed for a certain purpose. For example, some PCR tests can determine if a specific [virus](https://my.clevelandclinic.org/health/body/24861-virus) is present in the sample, which might be making you sick. Other PCR tests can determine if certain genes in your body might have important changes. Most of us know the term “PCR test” because of testing for [COVID-19](https://my.clevelandclinic.org/health/diseases/21214-coronavirus-covid-19). But it’s been used in medicine for a long time and has many other uses. Any test that uses a polymerase chain reaction technique is a PCR test. PCR is a type of nucleic acid amplification test (NAAT). ### What is a COVID-19 PCR test? Healthcare providers can use a PCR test to determine whether you have a COVID infection. They use a swab to get a sample of [mucus](https://my.clevelandclinic.org/health/body/mucus) or secretions from deep in your nose. PCR is then used to determine if genetic material (RNA) of SARS-CoV-2 (the virus that causes COVID) in your sample. ### What can PCR detect? Healthcare professionals perform PCR tests for many reasons. PCR can diagnose or detect: - [Infectious diseases](https://my.clevelandclinic.org/health/diseases/17724-infectious-diseases) (viruses, [bacteria](https://my.clevelandclinic.org/health/articles/24494-bacteria), fungi and [parasites](https://my.clevelandclinic.org/health/diseases/24911-parasites)) - Genetic diseases, like [cystic fibrosis](https://my.clevelandclinic.org/health/diseases/9358-cystic-fibrosis), Huntington’s disease, [fragile X syndrome](https://my.clevelandclinic.org/health/diseases/5476-fragile-x-syndrome) and others - Types of cancer, like [lymphoma](https://my.clevelandclinic.org/health/diseases/22225-lymphoma) - Gene changes (variations) in cancer that can be targeted with specific medications. - Gene changes that can put you at higher risk for certain diseases (like [genetic testing for cancer risk](https://my.clevelandclinic.org/health/diagnostics/23972-genetic-testing-cancer-risk)) - Gene changes in [prenatal testing](https://my.clevelandclinic.org/health/diagnostics/24136-pregnancy-genetic-testing) Advertisement Forensic labs can also use PCR to create detectable amounts of DNA found at crime scenes. ## Test Details ### What kind of tests or procedures use PCR? Many types of tests that use body fluids to look for genetic changes or infectious diseases use PCR. The type of test or procedure you need in order to get a sample depends on what you’re being tested for. Tests and procedures that use PCR include: - [Blood tests](https://my.clevelandclinic.org/health/diagnostics/24508-blood-tests). Providers use a sample of blood to look for gene changes and some infectious diseases. - [Nasopharyngeal swab](https://my.clevelandclinic.org/health/diagnostics/22878-nasopharyngeal-swab).A lab can use a sample of mucus from your nose to look for common infections, like influenza ([the flu](https://my.clevelandclinic.org/health/diseases/4335-influenza-flu)), COVID or respiratory syncytial virus ([RSV](https://my.clevelandclinic.org/health/diseases/rsv-respiratory-syncytial-virus)). - Preimplantation genetic diagnosis/PGD or preimplantation genetic screening/PGS. For preimplantation testing during [in vitro fertilization](https://my.clevelandclinic.org/health/treatments/22457-ivf) (IVF), a lab will test a few cells from embryos before implantation. This usually happens a few days after egg retrieval. - [Amniocentesis](https://my.clevelandclinic.org/health/diagnostics/4206-genetic-amniocentesis). Providers use a sample of [amniotic fluid](https://my.clevelandclinic.org/health/body/23310-amniotic-fluid) for [prenatal testing](https://my.clevelandclinic.org/health/diagnostics/24136-pregnancy-genetic-testing). - [Biopsy](https://my.clevelandclinic.org/health/diagnostics/15458-biopsy-overview). To diagnose genetic mutations in tumor cells (molecular testing), you’ll need a tumor or [bone marrow biopsy](https://my.clevelandclinic.org/health/diagnostics/17735-bone-marrow-biopsy). #### How to prepare for this test Most of the time, you don’t need to prepare for a PCR test. But it depends on what you’re being tested for and the procedure you’re having. Ask your healthcare provider if there’s anything you need to do before the test. ### How does it work? PCR identifies a very specific sequence of molecules that’s unique to the DNA it’s looking for (target DNA). For example, this sequence could be a specific gene change in a tumor or the genetic code of a virus or [bacteria](https://my.clevelandclinic.org/health/articles/24494-bacteria). The name “polymerase chain reaction” refers to how the lab amplifies (makes more copies of) the target DNA. It uses an [enzyme](https://my.clevelandclinic.org/health/articles/21532-enzymes) called DNA polymerase to build strings of DNA that copy the target DNA, if it’s present. The chain reaction happens when many cycles of heating and cooling a solution make more and more copies, potentially doubling the amount of target DNA each time. This means that PCR works with samples of DNA (or RNA) that are so small that they might be missed in other tests. Often, after PCR is complete, scientists might have to run other tests to analyze the sample — now with potentially millions of copies of the target DNA. Other times, the solution has labels that allow a healthcare professional to see whether the sample is positive or negative for the target DNA during the PCR amplification. In testing for infectious diseases, like viruses, this allows for quicker results, since you don’t need any additional testing. #### Types of PCR Some types of PCR require additional steps to amplify or analyze the target DNA: Advertisement - Reverse-transcriptase PCR (RT-PCR). Scientists use RT-PCR when the genetic information they want to copy is in the form of RNA rather than DNA. There are extra steps that make the RNA into complementary DNA (cDNA), so that a PCR can be performed. (Without this step, PCR can only be performed on DNA.) - Real-time PCR/quantitative PCR (Q-PCR). In real-time PCR, scientists add fluorescent labels to the DNA that mark the target DNA. This allows them to see whether the target DNA is in the sample without an additional test. Confusingly, some people also refer to this as “RT-PCR,” and it can also be combined with reverse-transcriptase PCR (real-time RT-PCR). Healthcare professionals use real-time RT-PCR for nasal swab tests for COVID-19 and the flu. SARS-CoV-2 (COVID-19) and influenza viruses are RNA viruses. Care at Cleveland Clinic [Get Cold, Flu & COVID-19 Care](https://my.clevelandclinic.org/services/cold-flu-covid-19-care) [Find a Walk-in Location Near You](https://my.clevelandclinic.org/services/cold-flu-covid-19-care#locations-panel) ## Results and Follow-Up ### What do the results of a PCR test mean? PCR tests might use different language in your results, depending on what you’re being tested for. For example, if your results say “detected” or “present,” it generally means you have the gene change or infection that the test was looking for. If the results say “not detected,” it means the test didn’t find the target DNA or RNA. In the case of an infection, this can sometimes mean that you were tested too early in an infection. You could still have an infection, but there weren’t enough viruses, bacteria or other diseases to be detectable, even with PCR. Advertisement #### What do COVID PCR test results mean? A positive COVID PCR test result — if you see the word “detected” on your result — means that it’s likely that you have COVID or that you’ve recently recovered from it. A negative (“not detected”) COVID PCR test result means you probably didn’t have COVID at the time of your nasal swab. But sometimes, PCR tests can be negative very early on in an infection, especially if you don’t have symptoms yet. #### When should I know the results of a PCR test? The results of nasal swab tests for common viruses like influenza and COVID usually take about a day to come back. The results of genetic testing through blood tests, biopsies and other procedures can take at least a week or longer. ### When should I call my doctor? Contact your healthcare provider if you have any questions about a PCR test or its results. ### A note from Cleveland Clinic The term “PCR test” suddenly became a part of everyday conversations with the COVID-19 pandemic back in 2020. But healthcare professionals have used PCR techniques for decades. By copying and detecting tiny amounts of DNA, PCR can help diagnose a variety of health conditions. But just because it’s routine for medical professionals doesn’t mean a test is routine for you. Fortunately, it only takes a small sample from your body to work, and your part is usually over in a few moments. Talk to your provider if you have any questions or concerns. 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Last updated on 01/21/2025. ### References Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards. - National Library of Medicine (U.S.). PCR Tests (https://medlineplus.gov/lab-tests/pcr-tests/). Updated 9/19/2024. Accessed 1/16/2025. - Waters DL, Shapter FM. The polymerase chain reaction (PCR): general methods (https://pubmed.ncbi.nlm.nih.gov/24243196/). Methods Mol Biol. 2014;1099:65-75. Accessed 1/16/2025. - Weil P. Molecular Genetics, Recombinant DNA, & Genomic Technology. In: Kennelly PJ, Botham KM, McGuinness OP, Rodwell VW, Weil P, eds. Harper’s Illustrated Biochemistry. 32nd ed. McGraw Hill Education; 2023. ### Care at Cleveland Clinic Cold, flu or COVID-19? 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Readable Markdown	### What kind of tests or procedures use PCR? Many types of tests that use body fluids to look for genetic changes or infectious diseases use PCR. The type of test or procedure you need in order to get a sample depends on what you’re being tested for. Tests and procedures that use PCR include: - [Blood tests](https://my.clevelandclinic.org/health/diagnostics/24508-blood-tests). Providers use a sample of blood to look for gene changes and some infectious diseases. - [Nasopharyngeal swab](https://my.clevelandclinic.org/health/diagnostics/22878-nasopharyngeal-swab).A lab can use a sample of mucus from your nose to look for common infections, like influenza ([the flu](https://my.clevelandclinic.org/health/diseases/4335-influenza-flu)), COVID or respiratory syncytial virus ([RSV](https://my.clevelandclinic.org/health/diseases/rsv-respiratory-syncytial-virus)). - Preimplantation genetic diagnosis/PGD or preimplantation genetic screening/PGS. For preimplantation testing during [in vitro fertilization](https://my.clevelandclinic.org/health/treatments/22457-ivf) (IVF), a lab will test a few cells from embryos before implantation. This usually happens a few days after egg retrieval. - [Amniocentesis](https://my.clevelandclinic.org/health/diagnostics/4206-genetic-amniocentesis). Providers use a sample of [amniotic fluid](https://my.clevelandclinic.org/health/body/23310-amniotic-fluid) for [prenatal testing](https://my.clevelandclinic.org/health/diagnostics/24136-pregnancy-genetic-testing). - [Biopsy](https://my.clevelandclinic.org/health/diagnostics/15458-biopsy-overview). To diagnose genetic mutations in tumor cells (molecular testing), you’ll need a tumor or [bone marrow biopsy](https://my.clevelandclinic.org/health/diagnostics/17735-bone-marrow-biopsy). #### How to prepare for this test Most of the time, you don’t need to prepare for a PCR test. But it depends on what you’re being tested for and the procedure you’re having. Ask your healthcare provider if there’s anything you need to do before the test. ### How does it work? PCR identifies a very specific sequence of molecules that’s unique to the DNA it’s looking for (target DNA). For example, this sequence could be a specific gene change in a tumor or the genetic code of a virus or [bacteria](https://my.clevelandclinic.org/health/articles/24494-bacteria). The name “polymerase chain reaction” refers to how the lab amplifies (makes more copies of) the target DNA. It uses an [enzyme](https://my.clevelandclinic.org/health/articles/21532-enzymes) called DNA polymerase to build strings of DNA that copy the target DNA, if it’s present. The chain reaction happens when many cycles of heating and cooling a solution make more and more copies, potentially doubling the amount of target DNA each time. This means that PCR works with samples of DNA (or RNA) that are so small that they might be missed in other tests. Often, after PCR is complete, scientists might have to run other tests to analyze the sample — now with potentially millions of copies of the target DNA. Other times, the solution has labels that allow a healthcare professional to see whether the sample is positive or negative for the target DNA during the PCR amplification. In testing for infectious diseases, like viruses, this allows for quicker results, since you don’t need any additional testing. #### Types of PCR Some types of PCR require additional steps to amplify or analyze the target DNA: - Reverse-transcriptase PCR (RT-PCR). Scientists use RT-PCR when the genetic information they want to copy is in the form of RNA rather than DNA. There are extra steps that make the RNA into complementary DNA (cDNA), so that a PCR can be performed. (Without this step, PCR can only be performed on DNA.) - Real-time PCR/quantitative PCR (Q-PCR). In real-time PCR, scientists add fluorescent labels to the DNA that mark the target DNA. This allows them to see whether the target DNA is in the sample without an additional test. Confusingly, some people also refer to this as “RT-PCR,” and it can also be combined with reverse-transcriptase PCR (real-time RT-PCR). Healthcare professionals use real-time RT-PCR for nasal swab tests for COVID-19 and the flu. SARS-CoV-2 (COVID-19) and influenza viruses are RNA viruses.
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