False Positive PCR - COVID-19 and possible reinfection when antibodies value is +7.0
A friend of mine was detected COVID-19 positive through PCR one month back. He was asymptotic as per doctors and had no symptoms.
He quarantined himself and increased his intake of water.
After 1 month, he got himself tested and the result was negative. His antibodies value was +7.0.
My question: Is it possible to get COVID-19 false positive ?
2) Is it possible that a person comes as COVID-19 positive due to bad sampling technique or something ?
3) Given the antibody value as 7.0. Is it possible that the same person gets COVID-19 positive again ?
(My theory is that COVID-19 will try to come to his body but his antibodies value is so high that it won't affect him.)
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The rt-PCR tests for Covid-19 are not 100% specific so yes it's possible to get a false positive.
From the China PCR test
The sensitivity of the RT-PCR diagnostic test was estimated to be 0.777 (95% CI: 0.715, 0.849), while the specificity was 0.988 (95% CI: 0.933, 1.000). The confidence intervals include sampling error in addition to the error due to probabilistic knowledge of the data.
This means that out of 100 true negative patients, the test will correctly identify 98.8 as negative.
Out of 100 true positive patients, the test will correctly identify 77.7 as positive. The positive predictive value (PPV, Given a positive test, what are the chances that the patient is actually positive) and negative predictive value however depend on the population sample that is being tested. This answer explains it fairly well.
We don't have enough data on antibodies yet to interpret them.
www.medrxiv.org/content/10.1101/2020.04.24.20078949v1
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