COVID-19 Tests

Types of COVID-19 viral tests

COVID-19 viral tests are diagnostic tests that can tell you whether you are currently infected with the virus that causes COVID-19 at the time of the test. COVID-19 viral diagnostic tests can be either antigen tests or molecular tests.

You may need to take a viral test:

  • If you have COVID-19 symptoms;
  • If you were exposed to someone who has COVID -19;
  • When you are referred to get tested by your healthcare provider, local health department, school, or work;
  • Before or after travel; or
  • For entrance to a venue, event, or activity.

Refer to the When Do I Use It? section below for additional details.

COVID-19 antigen tests

COVID-19 antigen tests look for the presence of specific SARS-CoV-2 virus protein structures (antigens) in a sample. Antigen tests can be less expensive than molecular tests and can give you rapid results- typically in less than 30 minutes.

Antigen tests are helpful in providing fast, generally reliable results when you have COVID-19 symptoms.  However, antigen tests are less sensitive than molecular tests; they may miss an early infection when there are low levels of virus in the body, also known as a false negative test result. 

Antigen tests can be administered in point-of-care settings (provided and interpreted by health care providers, testing facilities, pharmacies etc.), or sold online and at retail locations and administered at home (in self-test form).

COVID-19 molecular tests

COVID-19 molecular tests look for the presence of SARS-CoV-2 virus genetic material (nucleic acid or RNA fragments) in a sample. Molecular tests include PCR tests (reverse transcription polymerase chain reaction or RT-PCR), which are reliably accurate.

Molecular tests are more sensitive than an antigen tests; they can detect much smaller amounts of virus in the body, and therefore detect an infection earlier and can continue to detect remnants of the viral RNA in the body well after the infection has resolved.

Most molecular tests (e.g., PCR tests) are administered at a point-of-care site (e.g., health care provider, pharmacy, public health testing site, private lab). Most molecular tests must be processed in a laboratory so it may take hours to days to get your results.

Husky Coronavirus Testing, a UW voluntary research study, provides lab-processed PCR tests.

Antibody or serology tests are not viral tests and should not be used to diagnose a current infection.

Read the Public Health – Seattle & King County blog that further explains differences between rapid antigen tests and molecular PCR tests.

Comparison of PCR tests and antigen tests

Consider these factors when choosing between a molecular PCR test and an antigen test.


PCR test Antigen test

Viral diagnostic test processed by a lab from nasal or throat swab sample

Viral diagnostic test via nasal swab and test strip, processed at a point-of-care setting or acquired from a retailer and taken at home (self-test version)


PCR test Antigen test
Administered in a point-of-care setting (health care provider, pharmacy, public health testing site, private lab) Purchased over the counter and completed at home or completed at a point-of-care setting 


PCR test Antigen test

Hours or up to 3 days to process,

(depending on the lab)

15-30 minutes to process


PCR test Antigen test
  • Highly sensitive, highly specific test
  • Positive and negative results are highly reliable when used appropriately
  • Less sensitive test, but very accurate when a person has high viral levels/symptomatic and is likely to be most contagious 
  • May miss low levels of virus in a person, may show false negatives in asymptomatic people or in people in the first few days of their infection 
  • If your result is negative and your symptoms worsen (or you are concerned about a false negative result after a close contact or suspected exposure), take another antigen test within 24 to 48 hours or take a PCR test and isolate while you await results. 
  • Positive results are especially reliable if you have symptoms and during period of high transmission in the community.  
  • False positives can occasionally occur if the prevalence of infection in a community is low. 


PCR test Antigen test
  • Best for early diagnosis of an infection, even in asymptomatic people 
  • When you start developing COVID-19 symptoms (test after symptoms develop and isolate while awaiting your results)
  • At least 5 days after close contact exposure to someone with COVID-19 (If you test negative for COVID-19, consider testing again 1 to 2 days after your first test.)
  • Screening prior to a social gathering, activity, venue entrance or event, or before and after travel when you are symptom-free
  • If you need to confirm the results of an antigen test
  • For travel or venues/events requiring proof of vaccination, get an antigen or PCR test from a point of care or testing provider
  • Best for screening and rapidly identifying infectious individuals with symptoms and in high transmission settings
  • If you have COVID- 19 and have isolated for at least 5 full days and your symptoms are improved or you have no symptoms, and you want to check if you are still infectious before return to regular activities 
  • If you have recovered from COVID-19 within the last 90 days and you have a new COVID-19 exposure and develop new COVID-19 symptoms.
  • If you have symptoms and cannot get access to timely PCR testing: Take test the day AFTER symptoms develop or do 2 tests with at least 24 hours and no more than 48 hours apart if the first one is negative.
  • Rapid screening prior to a social gathering or activity when you are symptom-free (higher risk of false negative so continue to take additional precautions)
  • At least 5 days after close contact exposure (If you test negative for COVID-19, consider testing again 1 to 2 days after your first test.)
  • Multiple negative tests increase the confidence that you are not infected with the SARS-CoV-2 virus.
  • For travel or venues/events requiring proof of vaccination, get an antigen or PCR test from a point-of-care or testing provider


PCR test Antigen test
Do not get a PCR test if you had COVID-19 within the past 90 days (the test may be intermittently positive even after you are no longer infectious).

COVID‑19 self-tests (home tests) are not accepted:

  • To meet travel testing requirements
  • For entry to establishments or events requiring proof of vaccination

How to use a rapid antigen self-test

Watch the CDC video How to use a self-test and follow the instructions provided in the video.

Specific instructions are also provided in the self-test packaging, follow these specific instructions closely to best ensure an accurate result. 

Watch the CDC video How to interpret self-test results.

If you get a positive test result:

Get free rapid antigen self-test kits

Residential households in the U.S. can order free at-home COVID-19 self-test kits from the United States Postal Service (USPS) at kits or at Placing an order only requires your name and residential address. You may also share your email address to get updates on your order. No ID, credit card, or health insurance information is required.

Washington state residents can also order free COVID-19 at-home rapid self-test kits on the Say YES! COVID Test website. For questions related to the test itself or how to perform it, visit the Say Yes! COVID Test Digital Assistant or call 1-833-784-2588. If you have questions about the Say Yes! COVID Test program, visit the Frequently Asked Questions page or call the DOH COVID-19 hotline at 1-800-525-0127 (language assistance available). For questions about the Federal testing program, visit their Frequently Asked Questions page.

Tacoma -Pierce County Health Department maintains a list of where free home tests can be acquired at local libraries.

At-home tests can also be purchased online, and at local retailers and pharmacies. Be sure you are purchasing an FDA-approved COVID-19 test.  

PCR test locations

Testing locations that offer PCR tests are listed in the FAQ “I want to get tested for COVID-19. Where can I go?” on the University’s COVID-19 FAQ webpage.

If you need help finding a free COVID-19 testing site near you, check with your local health department or district. You may also call 1-800-525-0127.

Re-testing after you had COVID-19

Read the FAQ “Should I get tested again after testing positive for COVID-19?” on the Quarantine and Isolation Guidance webpage for information.

More information