What does the coronavirus test really look for? What does a positive test mean?
Dr. Frank McGeorge answers viewer question about coronavirus
DETROIT – There’s a lot of information and misinformation out there about the coronavirus, so Local 4 is letting viewers submit questions so we can find verified answers.
Dr. Frank McGeorge wants to verify or refute any information about the coronavirus, but there are also some questions experts still don’t know the answer to. McGeorge is discussing them because acknowledging what we don’t know is just as important as verifying information so people don’t rely on incorrect answers.
Doctors testing for coronavirus put a swab in the patient’s nose to get a sample of the cells and mucus in the area way back inside. They also routinely get a throat swab.
In many circumstances, other samples will be collected and sent to a lab.
Viewers from Dearborn to Troy have asked if the standard coronavirus test can tell if you have been infected but recovered.
The answer is no. The swabs are subjected to an advanced process called PCR, or polymerase chain reaction, test. It uses well-established technology to look for genetic material -- the RNA -- that’s specific to the new virus, SARS-COV-2, the cause of COVID-19.
If it is present, that means there is an active virus. Detection of the viral genetic material is dependent on collecting a good sample, which is why doctors swab thoroughly.
If the test is negative but the person actually has COVID-19, it’s called a false negative. There are several possible explanations for a false negative:
- The sample might not have been adequate.
- The test might have been faulty, which can happen a small percentage of the time.
- The person might be too early in their course and aren’t shedding enough viral particles to be detected.
- The person might have recovered and are no longer shedding particles.
These reasons are why in high-risk cases, the tests might be repeated.
The test doesn’t determine if you have previously been infected. Researchers have a blood test that determines if a person has developed antibodies to the virus. If positive, that would indicate exposure and recovery. This antibody test is not yet available for clinical use in the United States.
Once someone has been diagnosed with COVID-19, public health officials repeat the testing after recovery to ensure that sequential tests are negative and the individual is recovered.
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