COVID19 Diagnostic tests

By Dr Deepu Changappa Cheriamane


The definitive test for SARS-CoV-2 is the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) test. It is believed to be highly specific, but with sensitivity reported as low as 60-70% and as high as 95-97%. Meta-analysis has reported the pooled sensitivity of RT-PCR to be 89%. Thus, false negatives are a real clinical problem, and several negative tests might be required in a single case to be confident about excluding the disease.
Its sensitivity is predicated on time since exposure to SARS-CoV-2, with a false negative rate of 100% on the first day after exposure, dropping to 67% on the fourth day. On the day of symptom onset (~4 days after exposure) the false negative rate remains at 38%, and it reaches its nadir of 20% three days after symptoms begin (8 days post exposure). From this point on, the false negative rate starts to climb again reaching 66% on day 21 after exposure.

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