Repeat testing of persons who have a negative test may (eventually) confirm the presence of viral RNA, but this is impractical. Additionally, repeated testing of the same person can lead to
even more confusing results: The test may go from negative, to positive, then back to negative again as the immune system clears out the coronavirus infection and moves to recovery.
And what makes this testing even more confusing is that the FDA admits that "The detection of viral RNA by RT-PCR does not necessarily equate with an infectious virus."
Let's break that down:
You've had all the symptoms of COVID19, but your RT-PCR test for SARS-CoV-2 is negative.
•Does that mean you're "good to go" - you can go to work, go to school or you can travel? OR…
•Does that mean your influenza-like illness was caused by some other pathogen, possibly one of the four coronaviruses that have been in circulation for 60 years? OR…
•Does that mean the result is a false-negative and you still have the infection, but it isn't detectable by current tests? OR…
•Does that mean it was a sample was inadequately taken due to the faulty technique by the technician? OR…
•Does that mean you have not been exposed, and you are susceptible to contracting the infection, and you need to stay in quarantine?
So, what does a "positive" test actually mean?
And that's the problem:
No one knows for sure.
Another Type of Testing: Antibodies
According to the nonprofit Foundation for Innovative New Diagnostics (FIND), more than 200 serologic blood tests, to test for antibodies, are either now available or in development.
There are two primary types of antibodies that are assessed for nearly any type of infection: IgM and IgG. While several new testing devices are being touted as a home test, they are not the same as a home pregnancy test or a glucometer to you’re your blood sugar. The blood spot or saliva specimen can be collected at home, must it must then be sent to a laboratory for analysis. It can take a few days - or longer - to get the results. With so many tests in the pipeline, the ability to test at home will be changing over time.
The first antibody to rise is IgM. It rises quickly after the onset of the infection and is usually a sign of an acute, or current, infection. The IgM levels diminish quickly as the infection resolves. The FDA admits they do not know how long the IgM remains present for SARS-CoV-2 as the infection is being cleared.
The interpretation of an IgG antibody is more difficult. This antibody is an indicator of a past infection. The test is often not specific enough to determine if the past infection was caused by the SARS-CoV-2 virus or one of the four common coronaviruses that cause influenza-like illness.
Because serology testing can yield a negative test result even if the patient is actively infected (e.g., the body has not yet developed in response to the virus) or maybe falsely positive (e.g., if the antibody indicates a past infection by a different coronavirus), this type of testing should not be used to diagnose an acute or active COVID-19 infection.