Can a PCR test be false positive?

Posted by Jack on December 14, 2022
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    A false positive result is when a test says that you have a disease or illness when you don't actually have it. This can be very confusing and upsetting, but there are ways to determine whether or not your results are accurate. Here's how:

    False positives.

    If you have been exposed to other viruses that cause similar symptoms, such as the flu or measles, this can be a false positive. This is because these viruses share some similarities with herpes and are often mistaken for it.

    Also if your test turns out to be positive but you don't experience any symptoms, it could be a false positive. This happens when your body is exposed to the virus but then fights it off before any signs of an outbreak appear. If you're unsure about whether this applies to you, ask your doctor for help or advice about what steps might need taking next.

    If you have a reaction when getting your blood taken for the test (for example feeling faint), this may also mean that it's not accurate - so again talk to someone who can advise on what steps to take next.

    Another thing which can cause false positives is having received a transfusion of blood at some point in the last four weeks before getting tested (this means 14 days). Again speak with someone who knows more about these things than yourself before deciding whether further action needs taking now that we've established there could be a problem here!

    PCR testing.

    PCR (polymerase chain reaction) testing is one of the most accurate medical tests on the planet. It can detect minute quantities of DNA, and it's very sensitive. The more copies of a particular gene or piece of DNA you have, the stronger your signal will be when you test for it using PCR.

    It's not uncommon to get a false positive result with PCR testing—this happens in about 5% of all cases in which someone gets tested for COVID via PCR. A false positive means that your test results show that you have COVID when really you don't have any COVID at all; instead, some other virus or pathogen is causing your symptoms and making it look like your body has something wrong with it when really everything is healthy as can be!

    mRNA testing.

    mRNA testing is a more recent form of genetic testing, and it has several advantages over PCR. First, mRNA testing can detect DNA fragments as well as RNA fragments at the same time. Second, mRNA testing can also detect protein fragments—which means that if there are any cell membranes remaining in your sample after you've extracted the DNA or RNA from it, they too will be detected by an mRNA test. This makes it ideal for detecting viruses that have infected human cells because they can be found both inside and outside of those cells (and sometimes even within other viruses).

    Finally, whereas PCR works by amplifying small amounts of DNA or RNA into detectable quantities so that they can be analyzed further by other tests such as Polymerase Chain Reaction (PCR), mRNA is already present in large amounts—in fact, it's produced by every cell's nucleus at all times! Because mRNA is naturally abundant in our bodies but not always easy to extract using traditional methods like centrifugation/centrifugal sedimentation, this type of test may prove useful for detecting these molecules without having first extracted them from their source tissues first (which could damage them).

    Antigen tests.

    Antigen tests are used to detect antibodies in the blood. Antibodies are proteins produced by the immune system to fight foreign substances, such as viruses or bacteria. These tests are more specific than PCR tests and can be used to detect a specific strain of COVID. However, antigen tests tend to be more expensive than PCR tests and require additional equipment for accurate results.

    T issues.

    • T cell testing: T-cell testing is a blood test that looks for the presence of T cells in your blood. T-cell testing is not as reliable as PCR testing and may give false positives, depending on the type of T-cell that's tested.
    • False positive PCR results: The most common reason for false positive results on a PCR test is if you have been exposed to COVID at any time since your last vaccination. If this has happened, it will appear like you still have it even though you're immune to it now.

    Antibody testing.

    Antibodies are proteins produced by your immune system that can be measured in a blood test. Antibodies to the COVID virus will show up on this type of test, but they may not always be accurate.

    That’s because antibodies can also be made for other viruses that are similar to COVID, such as Epstein-Barr and cytomegalovirus (CMV). If you have one of these other viruses, it might mistakenly show up as if you had the COVID virus when really it’s something else entirely.

    A PCR can be a false positive but there are other tests that can help determine if you have COVID.

    The PCR test is not the only tool used to determine whether or not you have COVID. Other tests can be used to confirm a diagnosis, including:

    • Antigen tests – This type of test checks for COVID antigens in your blood. Antigen is the name given to a foreign object that triggers an immune response from your body. It’s similar to antibodies, which are also a sign of infection.
    • Antibody tests – These help doctors determine if there are antibodies present in your bloodstream as a result of an infection or other health condition like HIV/AIDS or cancer. They’re often used when diagnosing infections because it’s quicker than waiting for symptoms to appear and then confirming them through another test (like PCR).
    • mRNA testing – mRNA stands for messenger ribonucleic acid, which carries genetic information from DNA code from one cell nucleus into other parts called cytoplasm where proteins are created based on this code (in order words: genes).


    Remember, if you are experiencing a false positive result it is important to talk with your doctor about other testing options. You can also reach out to support groups for more information on COVID and its symptoms. We hope this article has helped answer some questions about COVID testing so that you feel confident in your next steps towards diagnosis or treatment options.

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