How is PCR used in testing infectious agents?

Posted by Jack on December 14, 2022
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    PCR stands for polymerase chain reaction. It is a laboratory technique used in the diagnosis of infectious diseases and genetic conditions, among other things. PCR uses an enzyme called DNA polymerase to make many copies of a specific segment of DNA. For this reason, it’s also known as “amplification” or “amplifying” because you get more DNA (and therefore information) out of your sample than you put in initially. The change we see in our sample is called an increase in quantity (also referred to as “quantitation”).

    What is PCR?

    PCR is a molecular biology technique used to amplify a specific piece of DNA. It is used in a wide variety of fields, including clinical medicine and environmental science. In PCR testing for infectious agents, the idea is to identify the presence or absence of an organism in a sample by amplifying its DNA with PCR. This can be done on many types of samples, from blood and body fluids to tissue cultures or swabs collected from surfaces like countertops and door handles.

    The benefits of using PCR testing include its accuracy, reliability, speed and ease-of-use—all at relatively low cost when compared to other methods.

    How is PCR used in diagnostic testing?

    PCR is a quick and accurate method of detecting the presence of an infectious agent in a sample. PCR can be used to detect a wide range of infectious agents, including viruses, bacteria and fungi.

    As PCR is less expensive than other methods such as ELISA (enzyme-linked immunosorbent assay), it is also cost-effective.

    Why use PCR over other testing methods?

    • PCR is more accurate than other methods: A number of tests are available to detect infectious agents, but PCR is more likely to give you accurate results.
    • PCR is more sensitive than other methods: It's possible to use PCR to detect very low levels of an infectious agent in a sample.
    • PCR is more specific than other methods: Other tests can sometimes confuse similar pathogens with one another. For example, if you have Lyme Disease and Epstein-Barr virus (EBV), the two infections are difficult to distinguish by looking at symptoms alone because they both have many overlapping symptoms. In this case, while it may seem smart to test for both types of infection simultaneously, doing so might lead you down the wrong path if your doctor happens upon some false positives from testing for EBV or other related viruses that don't cause Lyme disease—and vice versa! By using a single test like PCR instead of multiple tests together with varying degrees of accuracy and specificity for each pathogen present in the patient's samples, we can avoid this problem altogether by having a better idea about what we should look out for going forward."


    PCR is an amplification technique that allows you to use a sample from a patient to look for a particular infectious agent.

    With PCR, you take the sample and amplify it using two primers (which are short sequences of DNA). The process will start at the end of one primer and continue until it encounters the other primer, creating what looks like double stranded DNA. This process is repeated many times over until your sample has been amplified into millions or billions of copies!

    How long does it take to get a result from a sample processed by PCR?

    PCR is a fast test, with most results ready in hours or a day.

    If you're wondering how long it takes to get your PCR results back from the lab, know that:

    • Most labs process samples within 24 hours of receiving them.
    • Some labs can complete testing in as little as an hour.
    • Labs will usually send you your results via email or text message within 24 hours after processing is completed if not sooner (and some will even offer online access).

    What testing options are available for COVID-19?

    • PCR: The CDC recommends using the RealTime RT-PCR assay to test for COVID-19 infection ( This test detects the virus in blood, respiratory secretions and urine samples, and has been shown to be more sensitive than other methods used to diagnose acute infections with COVID-19.
    • Serology: A serology test detects antibodies against COVID-19 in a sample of blood serum or plasma taken from patients suspected of having been exposed to the virus during an outbreak or otherwise as part of routine testing.
    • Antigen detection: If a person has been infected with COVID-19 but does not have detectable levels of antibodies (either because it was not present or due to certain factors that affect antibody production), antigen detection tests may be used instead of serology tests for diagnosis purposes because they detect specific proteins produced by the virus itself rather than identify antibodies against those proteins that indicate past exposure or resistance, respectively.* Culture: Culturing viruses from patient specimens is another way doctors can determine if someone has been infected with an infectious agent such as CVID-19

    PCR allows for rapid, accurate and cost-effective screening of infectious agents.

    PCR is a powerful tool for the rapid, accurate, and cost-effective screening of infectious agents. It is used in conjunction with other tests such as culture or enzyme immunoassays to confirm the presence or absence of an agent. PCR may also be used in conjunction with molecular typing methods like restriction fragment length polymorphism (RFLP) or fluorescent amplified fragment length polymorphism (FAFLP) to determine whether a given strain isolated from a patient matches one previously identified by these techniques.

    • Methodology: PCR involves cycling between two major steps: denaturation and polymerization. In denaturation, DNA melts into single strands at high temperature (95°C), which allows primers that bind specifically to target regions on those strands to bind more efficiently. The cycle then begins again with polymerization where heat causes DNA molecules that have bound together from their complementary strands during denaturation to form new double-stranded molecules during synthesis at 72°C. This process repeats until enough copies are made for detection purposes.
    • How long does it take? Results typically become available within 2 hours after sample receipt in our laboratory; however, turnaround time will vary based upon specific testing needs (i.e., special requests).


    The method of PCR is a valuable tool for testing infectious agents. The technology allows for rapid, accurate and cost-effective screening of infectious agents. It has been used in clinical settings for the diagnosis of bacterial infections and viral diseases such as HIV.

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