01-08-2020  (313 lectures) Categoria: Medicina

Test for Past Infection

Test for Past Infection

Updated Feb. 2, 2021

Antibody or serology tests look for antibodies in your blood to determine if you had a past infection with the virus that causes COVID-19.

  • Antibodies are proteins created by your body’s immune system soon after you have been infected or vaccinated.
  • Antibodies help you fight off infections and can protect you from getting that disease again. How long this protection may last is different for each disease and each person.

Antibody tests should not be used to diagnose a current infection with the virus that causes COVID-19, except in instances in which viral testing is delayed. An antibody test may not show if you have a current infection because it can take 1–3 weeks after the infection for your body to make antibodies.

Whether you test positive or negative for COVID-19 on a viral or an antibody test, you still should take steps to protect yourself and others.

We do not know how much protection (immunity) antibodies to the virus might provide against getting infected again. Confirmed and suspected cases of reinfection have been reported, but remain rare. Scientists are working to understand this.

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How to get an antibody test

Decisions about testing are made by state or localexternal icon health departments or healthcare providers.​

Antibody tests for COVID-19 are available through healthcare providers and laboratories. Check with your healthcare provider to see if they offer antibody tests and whether you should get one.

What do your results mean?

If you test positive

  • A positive test result shows you may have antibodies from an infection with the virus that causes COVID-19. However, there is a chance that a positive result means you have antibodies from an infection with a different virus from the same family of viruses (called coronaviruses). Note: Other coronaviruses cannot produce a positive result on a viral test for SARS-CoV-2.
  • Having antibodies to the virus that causes COVID-19 may provide protection from getting infected with the virus again. But even if it does, we do not know how much protection the antibodies may provide or how long this protection may last. Confirmed and suspected cases of reinfection have been reported, but remain rare.
  • Talk with your healthcare provider about your test result and the type of test you took to understand what your result means. Your provider may suggest you take a second type of antibody test to see if the first test was accurate.
  • You should continue to protect yourself and others since you could get infected with the virus again.
    • If you work in a job where you wear personal protective equipment (PPE), continue wearing PPE.
  • You may test positive for antibodies even if you have never had symptoms of COVID-19. This can happen if you had an infection without symptoms, which is called an asymptomatic infection.

If you test negative

  • You may not have ever had COVID-19. Talk with your healthcare provider about your test result and the type of test you took to understand what your result means.
  • You could have a current infection or been recently infected.
    • The test may be negative because it typically takes 1–3 weeks after infection for your body to make antibodies. It’s possible you could still get sick if you have been exposed to the virus recently. This means you could still spread the virus.
    • Some people may take even longer to develop antibodies, and some people who are infected may not ever develop antibodies.

If you get symptoms after the antibody test, you might need another test called a viral test​. Viral tests identify the virus in samples from your respiratory system, such as a swab from the inside of your nose.

Regardless of whether you test positive or negative, the results do not confirm whether you are able to spread the virus that causes COVID-19. Until we know more, continue to take steps to protect yourself and others.

Learn more about using antibody tests to look for past infection.

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For healthcare professionals

For information on evaluating and testing for active infection, see recommendations for reporting, testing, and specimen collection.

For CDC interim guidance on antibody testing in clinical and public health settings, see Interim Guidelines for COVID-19 Antibody Testing.




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