07/06/2020
Diagnosis
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% 32 and as high as 95-97% 56. Meta-analysis has reported the pooled sensitivity of RT-PCR to be 89% 116. 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 (~ 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 138.
CT as diagnostic test
Multiple radiological organisations and learned societies have stated that CT should not be relied upon as a diagnostic/screening tool for COVID-19 52,57,87,88,116. On 16 March 2020, an American-Singaporean panel published that CT findings were not part of the diagnostic criteria for COVID-19 56. However, CT findings have been used controversially as a surrogate diagnostic test by some 2,32,89.
Markers
The most common ancillary laboratory findings in a study of 138 hospitalised patients were the following 13,89:
lymphopenia
increased prothrombin time (PT)
increased lactate dehydrogenase
Mild elevations of inflammatory markers (CRP 89 and ESR) and D-dimer are also seen.
