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What type of COVID-19 test should I get and when should I get it? What’s the difference between a PCR, antigen, and antibody test?

If you want to find out if you are currently infected with COVID-19, get a diagnostic test.

Testing is widely available and open to everyone.

It’s especially important to get tested if:

  • You have COVID-19 symptoms after being exposed, even if you are fully vaccinated or recently recovered from COVID-19 in the last 3 months.
  • You have been in close contact with someone who tested positive for COVID-19
  • You were recently in a large gathering where social distancing was hard to maintain or a crowded indoor setting and are not fully vaccinated or recently recovered.
  • You must travel and are not fully vaccinated, get a viral test 1-3 days before travel and 3-5 days after travel.

When should I get a COVID-19 test?

If you have had close contact exposure to a COVID-19 case or if you are concerned that you may have been exposed, the Department of Health recommends waiting 5 to 7 days after that initial exposure to get a diagnostic test due to the incubation period of the virus, the amount of the virus in your body, and the characteristics of diagnostic tests.

Which test should I get?

It is always best to talk with your health care provider about which test is best for you.

For people with symptoms, the most important thing to do is to get one of the two viral diagnostic tests.

If you have symptoms, get the quick antigen test if it is available. If it is positive, you can start isolating to protect those around you from the spread of the virus.

But if the antigen test is negative, you should get retested using a molecular (aka PCR) test and be sure to isolate yourself until you receive the result.

For most people who do not have symptoms but want to be tested because they may have been exposed, the molecular/PCR test is the better choice. It can find small amounts of the virus that might be seen before symptoms start.

What’s the difference between molecular/PCR, antigen, and antibody tests?

There are three different types of available coronavirus tests, and there are important differences between them.

Viral tests, which look for parts of the virus itself, are “diagnostic” – finding SARS-CoV-2 means that the person has COVID-19. There are two very different ways in which this is done.

Molecular/PCR Tests
A molecular test is usually performed using a technique known as Polymerase Chain Reaction (PCR), which works by rapidly making millions to billions of copies of viral-related DNA. If there are even small amounts of this genetic material in the sample, it will be detected. Thus, molecular/PCR tests are very sensitive and they are also very specific. A positive test is almost never wrong in determining that SARS-CoV-2 is present. Tests can be done on samples taken by nasal or throat swabs, and even by saliva.

However, since molecular/PCR tests are almost always performed in specialized labs, it is a relatively slow process. Results on tests done as an outpatient are rarely ready in less than a day and may take much longer.

Antigen Tests
The other viral test is an antigen test, which is much simpler and can be done in many doctor’s offices using a nasal or throat swab. In the future, it might even be able to be done at home or in other non-medical settings.

An antigen test is fast – providing results in minutes. But there is a catch: It is much less sensitive than the molecular/PCR test. There needs to be more virus present before the test will turn positive. This means that an antigen test may sometimes be falsely negative, meaning a negative result cannot always be trusted. A positive test, suggesting that the virus is present, is usually reliable, although even here false positives are more likely than with a molecular/PCR test.

Antibody Tests
An antibody test looks for the body’s response to SARS-CoV-2, the virus that causes COVID-19. It is a blood test that is good at determining if you had the disease, but not good for determining if you have the disease. As such, antibody tests should not be used to diagnose the virus.

While there is evidence that antibodies may provide protection from infection, that has not yet been proven and therefore results of an antibody test should not be used to determine immunity.