Get the right type of COVID-19 test

Illustration of nasopharyngeal Covid-19 PCR test

In this post, we are going to dive into the difference between types of COVID tests. This is important because different tests are appropriate for different circumstances, depending on accuracy, result time, and whether you may be currently or previously infected. 

The science behind COVID-19 testing can be hard to decipher. We want to make it easy for you to decide which test is right for you by giving you the basic rundown on each type of test. By the end of this article you'll know more about what tests are available and which test is right for you. 

Why get tested?

Generally, people get tested for reasons like these:

  • To diagnose illness after suspected exposure
  • To help confirm non-infection before travel or other event
  • To keep ourselves and our community healthy by tracking the spread of the virus 

The CDC recommends testing for COVID-19 if you have close contact with someone with positive diagnosis, or if you are showing symptoms. 

PCR testing

What it is

Also known as a qRT-PCR test (real-time quantitative reverse transcription polymerase chain reaction) or NAAT (nucleic acid amplification test), this type of molecular diagnostic test confirms current infection by detecting the presence of genetic material from the virus that causes COVID-19. PCR tests are effective because they are able to detect very small concentrations of the virus other tests might not catch.

How it works

PCR tests replicate the DNA or RNA of the viral genetic material in your body and test it against a control sample of SARS-CoV-2 in a lab. Often samples will be taken via a pharyngeal aka nasal swab. Lucky for us, there are next generation tests available that have high concordance and efficiency using a saliva sample.

This test is least accurate immediately after exposure to the virus. For greatest accuracy, you should isolate for five to seven days before being tested.

Why use it

PCR testing is the most accurate type of test available. Results are generally available within one to three days.

Antigen testing

What it is

Antigen tests look for the presence of detect the presence of a specific viral antigen, which implies current viral infection.

How it works

It looks for a specific protein to indicate the presence of infection. Antigen testing is less accurate than PCR testing. If you test positive initially with this kind of test, you will need to get a confirmatory PCR test.

Why use it

Antigen tests are rapid, often providing results in minutes. They are less expensive than PCR tests. Some antigen tests have been approved for testing as home kits. 

Antibody testing

What it is

An antibody test, also known as a serology test, finds proteins made in your body in response to previous infection or from vaccination for COVID-19. There are neutralizing antibodies which defend our bodies from infection and non-reactive non-neutralizing antibodies which do not. 

Antibody tests cannot diagnose current infection. 

How it works

Your blood is tested for proteins created by your body’s immune system soon after you have been infected or vaccinated.

Why use it

 If you’re traveling to China, you will need a total antibody test which tests for both kinds of antibodies neutralizing and non-neutralizing.

If you are trying to determine if you have potential immunity or whether you have been infected in the past you will need a neutralizing antibody assay. 

Even if you do have COVID-19 antibodies, we do not know yet if this provides any length of immunity. Please continue to take these safety precautions seriously. 

Compare the tests

Type of test What it does How accurate is it? When to get it
PCR Tests for current infection Most accurate If you are symptomatic or exposed to COVID-19
Antigen Rapidly tests for current infection Less accurate than PCR For a quick, inexpensive, at-home test if PCR is not available
Antibody test
Neutralizing
Tests for prior infection Less accurate than PCR To confirm previous infection
Antibody test
non-neutralizing and non-reactive
Tests for both kinds of antibody responses Less accurate than PCR If you want to go to China


What if the test is inaccurate? 

You may be wondering why use tests that don’t provide 100% accuracy. The simple answer is that no such test exists. We need to combine medical care with observation, common sense, and updated information for our best chances at staying healthy. 

Test accuracy is influenced by the type of test and when you were tested relative to your exposure. For a deeper dive into the accuracy of each test, visit Harvard Health.

False positives

Sometimes the test tells us we have COVID-19 when we actually don't. These false results are generally due to human error or lab contamination. If you receive a positive test result from any type of test, get a confirmatory PCR test immediately

False negatives

More commonly, a test indicates we are not infected with COVID-19 when we might actually be. These sometimes occur when there is not enough virus in a given sample for the test to be accurate. 

The COVID-19 virus takes several days to incubate in your system before it can be reliably tested with either the PCR or the antigen test. It is best to get tested three to five days after known exposure. We talk more about the viral time-table here. 

Conclusion

Now you know that PCR testing is the gold standard for COVID diagnostic testing, with the highest accuracy available. Both PCR and antigen testing identify current infection. Generally, you want to seek out a PCR test and settle for an antigen test in its absence. 

Use an antibody test to confirm prior infection. Remember you may not have developed antibodies, and even if you did it might not confirm immunity. 

In the USA, tests must be ordered by your healthcare provider. For info on how to source low-cost or free testing, learn more about how to pay for COVID testing

We hope you find this useful! Please remember to stay safe, wash your hands, wear your mask, and get tested. 

Garrett Christopher

Garrett Christopher is a writer, artist and plant geek living in Portland OR. He helps brands and businesses create engaging, clear, and creative content. Omnivorous with a taste for the odd and captivating he writes about current events, the arts and culture.

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