SARS-CoV-2 Infection: Updates on laboratory diagnosis

The response of laboratory medicine to the SARS-CoV-2 pandemic has been very fast and comprehensive. Direct detection of viral RNA by different nucleic acid amplification techniques is recommended. While it allows for a diagnosis of COVID-19 disease in the early stages, patients admitted late may test negative on swabs taken from the upper respiratory tract. The early rise of humoral immune response may allow for an etiological diagnosis in such cases; IgG and IgM antibody response mounts early and peaks in the late stages of the disease, with specific IgG lasting longer after recovery, so the detection of the two Ig classes shall allow for both a timely diagnosis and to define the stage of infection. The main targets for the antibody response are the antigens from the nucleocapsid (N) and spike (S) domains, and the former appear to elicit an earlier response. While the role antibodies play in generating a true protective immunity is yet to be clarified, several evidences indicate that a strong humoral response correlates with viral neutralization. Finally, the combination of RNA and antibody detection shall be useful in all the potential testing scenarios. For serology, while clinical sensitivity is relevant for diagnosis, a high specificity is crucial to guarantee a high positive predictive value when asymptomatic populations are screened.

 

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