I tested positive with covidSHIELD and negative with nasal PCR or other test. Which result is correct?
Not all PCR tests are the same. They run on different PCR instruments, use different reagents, look for different genes, etc. etc. For example, the covidSHIELD saliva test is more reliable overall compared to self-collected nasal specimens. Nasal PCR has a higher false/negative rate and lower sensitivity in most studies. The covidSHIELD test is also much more accurate than antigen (sometimes referred to as "rapid") tests.
Proving a specimen is negative is more difficult than proving it is positive. A positive covidSHIELD test means that, at a minimum, two genes unique to SARS-CoV-2 were detected in the specimen. A negative test is technically “not detected” which means there could be SARS-CoV-2 there but we couldn’t find it. I always give this silly analogy: If I looked out my window and saw a dinosaur in my yard, I would be positive there is a dinosaur in my yard. If I looked out my window and didn’t see a dinosaur in my yard, that doesn’t mean there isn’t one there. It might just be somewhere I can’t see through the window. A specimen that tests positive for SARS-CoV-2 with covidSHIELD had the virus in the sample that was tested. We saw the dinosaur.
In short, a positive result from covidSHIELD should be treated like a positive. Your healthcare provider or local health department can help you to determine what that means for you.
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