Public Health

COVID-19 Antibody, PCR, and Rapid Test Results Explained

Khang T. Vuong24 Nov 2020

COVID-19 Antibody, PCR, and Rapid Test Results Explained

 

Quick Digest: 

  • The two main types of COVID-19 tests are diagnostic tests (PCR and antigen) and antibody tests
  • While diagnostic tests detect an active COVID-19 infection, antibody tests detect past infection with COVID-19
  • A membership with Mira can help you get discounted laboratory tests, such as the antibody test
  • If you have no insurance or have a high deductible, Mira is a good option to get access to a free at-home COVID test.

 

What are the different types of COVID-19 tests? 

There are two main types of tests for COVID-19: diagnostic tests and antibody tests. 

Diagnostic tests can detect whether or not you have an active infection of COVID-19. There are two categories of diagnostic tests, molecular PCR tests, and rapid antigen tests. 

Molecular PCR TestsRapid Antigen Tests
May need to wait a few days or up to one week for results May be able to get results within one hour
A sample is collected through a nasal swab or saliva  A sample is collected through a nasal swab
More accurate results (lower chance of a false-negative) Less accurate results (negative test may need to be confirmed with a PCR test) 

Antibody (serology) tests detect the previous infection with COVID-19 but do not show if you are currently infected. If you had the coronavirus, your immune system may have produced antibodies to fight the infection. The common antibody test detects IgG antibodies. Antibody tests are completed by collecting a blood sample and results are typically available within 1-3 days. 

 

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When should I get a diagnostic or antibody test? 

In the graphic below, we outline when you should consider getting a PCR, antigen, and antibody test for COVID-19. If you want to see if you were previously infected with COVID-19, you should get an antibody test. If you need a test for travel purposes, most states ask for a PCR test; however, a few states will accept an antigen test as well. 

If you had recent exposure to someone who has COVID-19 or has symptoms, you should get a diagnostic test. An antigen test will give you results faster, but the results of a PCR test are more accurate. If you get a negative antigen test, you should confirm these results by getting a PCR test as well. 

What Type of COVID-19 Test Should I Get? 

 

COVID Test Results Explained

 

What do the results of an antibody test mean? 

What does it mean if my antibody test is positive?

A positive test result means that you were likely previously infected with the virus that causes COVID-19. It is currently unknown whether the COVID-19 antibodies can protect you from being reinfected. Researchers are still trying to figure out what quantity and type of antibodies a person needs to be immune to COVID-19. 

Therefore, if you have the COVID-19 antibodies, you are not immune to COVID-19 and you should continue to wear a cloth face covering, practice social distancing, and have good hygiene. 

What does it mean if my antibody test is negative?

A negative test result means that you most likely were not previously infected with COVID-19. If you recently had COVID-19, you should wait about three weeks before getting the antibody test, as it can take 1-3 weeks for the body to produce antibodies. 

What does it mean if my antibody test is equivocal?

An equivocal test result is neither positive nor negative. You may get this test result if you have antibodies for a common cold that is similar to COVID-19 or if your body hasn’t produced enough antibodies yet. You may want to get retested in a few weeks for a more accurate result.

 

What do the results of a diagnostic (PCR or rapid) test mean? 

What does it mean if my diagnostic test is positive?

A positive test result on a diagnostic test means that the virus that causes COVID-19 was detected and you have a current infection. It is important that you notify close contacts of your positive result and isolate immediately. There is an extremely low chance of getting a false-positive result. 

In general, if you do not have symptoms, you need to isolate yourself from others for 10 days after receiving a positive result. If you have symptoms, you need to isolate yourself from others for 10 days after symptoms onset. You should only see others if you have not had a fever for at least 24 hours with no medication and your other symptoms are improving. See our article for more information on how long you are contagious with COVID-19. 

What does it mean if my diagnostic test is negative?

A negative test result means that the virus that causes COVID-19 was not detected in your sample. If you were tested due to recent exposure to someone who has COVID-19, you should remain in quarantine for 14 days even if you have a negative test result. It is possible that you still have COVID-19 but your sample was taken too early in the course of your illness. 

It is important to note that all diagnostic tests may yield false-negative results, so it is still possible to have COVID-19 and get a negative test result. If your negative result is from an antigen test, you may want to follow up with a PCR test for more accurate results. 

What does it mean if my diagnostic test is inconclusive?

An inconclusive test result likely means that a small amount of viral material, but not enough to yield a positive result. You should isolate yourself from others and get retested for more accurate results. 

 

How long after exposure should I get an antibody or diagnostic test?

Since the antibody test assesses past infection, you should not get a test if you currently have symptoms of COVID-19. According to the Centers for Disease Control (CDC), it typically takes at least 1-3 weeks after getting sick for a patient to develop the antibodies for COVID-19. 

If you were exposed to someone with COVID-19, you should aim to get a diagnostic test about 5 days after exposure. Read more about when to get a COVID test here. Do not get the diagnostic test the same day you were exposed, as your results will not be accurate. Your COVID-19 diagnostic test should be accurate if you are currently presenting with symptoms. 

When to Get Each Test: https://coronavirusexplained.ukri.org/en/article/vdt0006/

 

Antigens vs. Antibodies

An antigen is any substance or organism that is unrecognized by our immune system. Our immune system has “memory” which allows the system to deal with the offending antigen much more quickly and efficiently the next time it is encountered. 

Antibodies are proteins that bind with the antigen in order to neutralize the latter – or make other elements of the immune system “aware” of their presence. 

Vaccinations need both, antigens and antibodies in order to be effective. An antigen is a disease agent (virus, toxin, bacterium parasite, fungus, chemical, etc) that the body needs to remove, and an antibody is a protein that binds to the antigen to allow our immune system to identify and deal with it.

 

How accurate is the antibody test? 

In order to be approved, antibodies must have a sensitivity of 90% and specificity of 95%. Sensitivity is the ability for a test to detect a true positive result (presence of the antibodies) and specificity is the ability for the test to detect a true negative result (the absence of antibodies). 

This all means that even if you test positive, there is still a chance that your results are a false positive. In fact, in areas where there is a low prevalence of COVID-19, the number of false-positive tests has been nearly the same as the number of true positives. Before getting an antibody test, research the type of test that you will get and its accuracy. Some of the more accurate tests include those developed by Mount Sinai Hospital and Roche Holding AG. 

 

Where to get antibody or diagnostic tests for COVID-19 

  • A membership with Mira gives you access to low-cost laboratory tests, including the COVID-19 antibody test. In addition, a membership with Mira can help you get access to an at-home PCR test for free.
  • Rapid testing locations in NYC 
  • Primary health care provider
  • Laboratories, such as LabCorp and Quest
  • Urgent care facilities such as CityMD

 

For more information on COVID-19 testing locations in your city, see our articles:

How and Where to Get Tested in Philadelphia

How and Where to Get Tested in Chicago

How and Where to Get Tested in New Orleans

How and Where to Get Tested in San Fransisco

How and Where to Get Tested in Houston

How and Where to Get Tested in Los Angeles

How and Where to Get Tested in Honolulu

How and Where to Get Tested in NYC

 

Sources:

https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html#:~:text=Antibody%20tests%20check%20your%20blood,COVID%2D19%20infection.

https://www.wsj.com/articles/tested-positive-for-coronavirus-antibodies-dont-let-your-guard-down-11591794007

https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics

https://www.citymd.com/news/understanding-covid-19-results

https://coronavirus.medium.com/so-you-got-your-antibody-test-results-back-now-what-9630c633ffb1

https://medical.mit.edu/covid-19-updates/2020/06/how-accurate-diagnostic-tests-covid-19

https://www.gideononline.com/2020/10/01/antigen-vs-antibody-what-is-the-difference/

https://www.citymd.com/news/covid-19-testing-update

https://newsroom.questdiagnostics.com/2020-04-28-Quest-Diagnostics-Launches-Consumer-Initiated-COVID-19-Antibody-Test-Through-QuestDirect-TM

https://www.aamc.org/news-insights/your-covid-19-testing-questions-answered
 

 

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