Laboratory methods for diagnosing COVID-19 follow two pathways:
- Detection of the coronavirus itself, and
- Detection of the body's adaptive immune response to the virus.
The stage of COVID-19 disease progression determines which detection method is most effective. The rapid diagnostic (RDT) test complements nucleic acid methods such as RT-PCR to improve speed of diagnosis and monitor disease progression. As the disease primarily attacks the lungs, specimens taken from the upper respiratory tract may be poor in quality and could lead to false-negatives with PCR.
To understand the clinical significance of results obtained from the RDT, the following information must be considered:
- The median incubation period is estimated to be 5.1 days.
- Specific IgM antibodies to SARS-CoV-2 become detectable 3-5 days after onset of symptoms.
Therefore, the RDT should not be used until symptoms have been present for at least 3 days.
