COVID-19 Testing Frequently Asked Questions For Patients
PCR Testing (Diagnostic Testing)
What does the PCR test detect?
- The PCR (polymerase chain reaction) test detects the presence of RNA (genetic material) from the SARS-CoV-2 virus that causes COVID-19. One of the testing platforms used by UW Virology is a transcription mediated amplification (TMA) assay, which is technically not a PCR method but uses a similar principle of exponential amplification.
- These tests are considered diagnostic tests, as they are used to detect current infection with the virus (as opposed to past infection which may be detected with an antibody test).
Is the SARS-CoV-2 PCR test offered by UW Virology a nucleic acid amplification test (NAAT)?
Yes, PCR is the most commonly used NAAT technique for detecting specific nucleic acid in a sample. NAAT techniques such as PCR and TMA are both sensitive and specific for detecting the presence of SARS-CoV-2 in a sample. This contrasts with antigen testing which detects a specific viral protein in a sample. Antigen tests are more rapid but than PCR tests but may not detect all infections (less sensitive) and are more susceptible to false positive results (less specific).
I have symptoms that I think might be COVID-19. Should I get the PCR test?
Yes. The PCR test detects the SARS-CoV-2 virus and is used to diagnose acute infections. If you have any symptoms concerning for COVID-19 (fever, feeling short of breath, cough, muscle pain, sore throat, loss of taste or smell, new diarrhea) you should talk to your provider about getting PCR testing. If you do not have a primary care provider and/or are having difficulty finding testing in the King County region, refer to this list of community testing sites: King County testing locations.
What does a positive PCR test result mean?
A positive PCR result indicates that viral nucleic acid is present in the sample. Given both the potential severity of the infection and the potential for rapid spread, positive results should generally be treated as if the someone is infectious, with isolation to prevent spread and clinical care if symptoms warrant it. Individuals may test positive for weeks or even months after their first positive test even though they are not infectious. Repeat testing after the first positive test is generally not indicated.
What does an “inconclusive” result mean?
Many PCR tests target two or more distinct gene regions of the virus. When all targets are not detected above the threshold for positivity, the test is resulted as inconclusive. This typically happens when a low amount of viral nucleic acid is present. This should be treated as a presumptive positive and guidelines for isolation and clinical management based on a positive test should be followed.
Is the UW Virology Laboratory a CLIA-certified laboratory?
Yes. CLIA certification is a requirement for clinical laboratories providing diagnostic testing.
Have the PCR tests offered by the UW Virology Laboratory been granted Emergency Use Authorization (EUA)?
Yes. The tests performed by the UW Virology Laboratory have been granted Emergency Use Authorization (EUA) by either the FDA or Washington state.
Antibody Testing (Serology Testing)
What is an antibody?
- An antibody is protein that is a normal part of the immune response to many types of infections.
- Our bodies develop antibodies in the days and weeks after being infected.
- Antibodies are specific for different infections – as part of the immune response, the antibody attaches to specific parts of the germ. For example, there are antibodies for influenza and different antibodies for hepatitis C.
What is an antibody test?
- An antibody test is a type of blood test to see if you have:
- Any antibodies for an infection (yes/no result also known as a “qualitative” test), or
- How much antibody (a “quantitative” test)
- These tests are also referred to as “serological” tests.
Does UW Medicine have an antibody test for COVID-19?
- Yes, UW Medicine has a test that looks for antibodies to SARS-CoV-2, the virus that causes COVID-19.
- The test is a “qualitative” test; it only can tell you if it detects antibodies to SARS-CoV-2 or not. It does not provide information on how much antibody there may be.
How accurate is the antibody test?
- It is very sensitive – validation by our laboratory showed that by fourteen days after a positive acute COVID-19 diagnostic test (PCR) 100% of patients have a positive antibody test.
- It is very specific – it will be negative in >99.9% of people who did not have an infection.
- One challenge with this test is that due to the overall low number of people with COVID-19 in the community, it is possible to have a “false positive” result. This means the test will be positive when the person never was infected. This is true for all antibody tests, including a very good one like the one used at UW Medicine.
- In some cases, immunocompromised patients may have a negative test result despite prior COVID-19 infection due to lack of or delay in development of detectable antibodies.
I have symptoms that I think might be COVID-19. Should I get the antibody test?
- No. The antibody test is not used to diagnose acute infections. If you have any symptoms concerning for COVID-19 (fever, feeling short of breath, cough, muscle pain, sore throat, loss of taste or smell, new diarrhea) you should talk to your provider about getting a different test (usually a PCR) that looks for the virus itself.
- Because antibodies do not develop days to weeks after infection, we cannot depend on them for diagnosis.
I want to get tested to see if I had COVID-19. Can I just go to a hospital or clinic and get tested?
No. You should talk to your provider to learn about the test and to determine whether you should get this test. The test requires an order from your provider and then a blood draw by a qualified healthcare professional.
If not used for diagnosis of COVID-19, why would I get an antibody test?
- The antibody test can confirm that you had a past COVID-19 infection if you had COVID-19 symptoms (fever, tiredness, dry cough, aches and pains, sore throat, diarrhea) more than two weeks ago but were not able to access diagnostic PCR testing to confirm the infection.
- If your test is negative (and you have no symptoms), it means you likely have not had a COVID-19 infection and lets you know that you have no immunity to SARS-CoV-2.
- If your test is positive, it is likely that you were infected at some point in the last several months, but the result may also be a “false positive” (discussed above). This means that result is positive even though you were not exposed to the virus.
- This type of test will help public health departments and researchers learn more about how many people in a population have been exposed or infected.
- If you are interested in getting tested, you should discuss with your provider.
Does a positive antibody test result mean I am immune?
- We do not yet know if a positive test result means that a person is immune, and if it does, for how long immunity might last. We hope to learn more about these questions in the coming months.
- If your test is positive, you should continue to follow public health recommendations on social/physical distancing, hand hygiene, environmental cleaning, staying home when ill and mask use.
I think I had COVID-19 and want to be a plasma donor or participate in a clinical trial, should I get this antibody test?
Please contact your provider to discuss your eligibility to donate plasma and whether testing is indicated. If you have already had COVID-19 antibody testing, tested positive, and are interested in donating plasma, please email firstname.lastname@example.org with your name, your phone number, the date you started having symptoms of the illness, and the date your antibody test was positive. For more information, please visit: https://newsroom.uw.edu/news/plasma-donors-sought-among-those-recovered-covid-19.
Technical information on the UW Medicine antibody test:
- UW Virology is performing the Abbott SARS-CoV-2 IgG immunoassay on the ARCHITECT instrument. This is a chemiluminescent microparticle immunoassay (CMIA) used for the qualitative detection of IgG antibodies to SARS-CoV-2 nucleocapsid protein in human serum and plasma. This is a high-throughput automated system allowing for the testing of thousands of samples each day.
- The Abbott SARS-CoV-2 IgG immunoassay detects antibodies to the viral nucleocapsid protein (NP).
- The results are either “positive” or “negative” based on the manufacturer-indicated cutoff.
- A negative result indicates that either a person has not been infected with SARS-CoV-2 or there is not a detectable level of antibody present. Explanations for this may include a very recent exposure such that not enough time has elapsed to generate an immune response, or the immune response has decreased below the detectable level. A negative result does not rule out current or past infection with SARS-CoV-2.
- A positive result likely indicates previous or current infection. Recent studies examining serial plasma samples in hospitalized patients with SARS-CoV-2 infection suggest that the median time to seroconversion is about ten days in moderately ill patients, and fourteen days in severely ill patients. It is important to note that a positive serology test cannot distinguish between active or past COVID-19. If there is concern for active infection, molecular testing (PCR) with a nasopharyngeal swab is recommended.
- Due to an overall low absolute prevalence of SARS-CoV-2 infection locally, false positives will occur.
- At this time, it is not known whether the presence of antibodies confers protection from reinfection with SARS-CoV-2, how long the antibody response lasts, or the association between antibody response and clinical outcomes of individuals with COVID-19.
|NCVIGG||COVID-19 Antibody (IgG)||Blood|
|NCVQLT||SARS-CoV-2 (COVID-19) Qualitative PCR||nasopharyngeal (NP) or oropharyngeal (OP...|
Last updated 2020-11-03T04:47:52.041028+00:00