Antibody testing

PCR tests (also known as “molecular tests”) are the gold standard in Covid-19 testing. PCR is the most reliable and widely available testing method.

Rapid antibody tests have three steps:

  1. A blood sample is taken from the patient, either through a regular blood draw or through a finger stick.
  2. The blood sample will be applied to a test strip and exposed to a small sample of the virus’s antigens, which will “simulate” the presence of Covid-19 in the blood.
  3. After a couple of minutes, the test strip will show whether SARS-CoV-2 antibodies are present.

Rapid testing usually takes 15-30 minutes. The procedure is very similar to antigen testing, as it involves a test strip and results are easy to visualize.

The Science

When you’re infected with a virus, the virus will thrive by creating copies of itself, which will spread through your body. In the case of Covid-19, these virus cells will mostly concentrate in the respiratory system. That’s why diagnostic tests usually take samples from the respiratory canal: That’s where the virus’s genetic material is bound to be.

When the immune system detects a viral attack, it produces proteins called “antibodies”. These antibodies bind to a virus to prevent it from creating copies of itself.

Through a test sample, an antibody test will detect two types of antibodies:

  • The antibodies that your immune system produces in the first days of the infection (IgM)
  • The antibodies that exist in your bloodstream to protect you in the future (IgG and IgA).

There are two types of antibody tests: Qualitative tests and quantitative tests. Qualitative tests give a positive or negative result. They’re great for determining whether you’ve had Covid-19 in the past. Quantitative tests, on the other hand, determine the concentration of antibodies in your blood.

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Frequently asked questions

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How accurate are antibody tests?

Antibody production takes time and can vary through time. While accuracy can vary depending on the stage of the infection, antibody tests are generally very accurate.

One study found that antibody tests conducted 3-5 weeks after symptoms appeared had a 90-98% sensitivity, meaning they detected antibodies in 90-98% of samples that actually had antibodies. And many tests have a reported 100% specificity. It’s nearly impossible to obtain a false-positive result for an antibody test.

Can I get tested for antibodies while I’m sick with Covid-19?

It’s not advisable to visit a testing location while infected. On the other hand, antibodies are usually at their peak 2-5 weeks after the patient has developed symptoms. Thus, there is a considerable chance of testing negative for antibodies while still symptomatic. While you should check with your healthcare provider, many locations suggest getting tested for antibodies, 5 weeks after showing Covid-19 symptoms.

What are the benefits of antibody testing?

There are a few benefits to antibody testing. While we do not yet know how long antibodies will remain after infection with SARS-CoV-2, producing antibodies against the Coronavirus does likely offer protection from symptomatic disease if re-infected.

Producing antibodies does not mean you won’t get infected again. It does mean, though, that your body is more likely to handle the viral infection quickly and prevent severe symptoms. Another benefit to antibody testing is that communities that track antibody test results have a fuller picture of the prevalence of SARS-CoV-2 in their area. This can help guide public health decisions.

If I got vaccinated for Covid-19, will I test positive on an antibody test?

Yes, and it’s great news! Vaccines work by giving your body a reference of how the virus “looks”, so you can produce the antibodies to counter it. If you test positive on an antibody test, there’s nothing to worry about. It’s just the vaccine doing its job. However, vaccination shouldn’t cause you to test positive on a diagnostic test such as PCR.