It was inevitable that companies would start pushing out tests for measuring antibodies to SARS-CoV-2. There has been a lot of discussion in our professional circles about the status of these assays and whether there is value to use them in the current situation. Here are four of the most salient points from these discussions to keep in mind:

• Serologic testing questions are raised frequently by clinicians and administrators, especially as more and more manufacturers are developing rapid point-of-care ("POC") tests. However, these are detailed indiscriminately to providers, and there are no guidelines or recommendations from any professional group on the utility of serologic testing.
   
• Studies suggest that most patients seroconvert (both IgM and IgG) anywhere from 8 to 11 days post-symptom onset (consistent with most other seroconversion timelines), so the idea that a serologic test can be used at the point-of-care to diagnose -- or to rule out -- acutely symptomatic patients is wrong. Some studies also suggest that viral shedding may still occur in the presence of an antibody response.
   
• There are no definitions of "immune status," so the mere presence of antibodies as measured by a serologic test cannot be used for determining whether or not, for example, an individual can return to work or can safely work around infected individuals. 
   
• The performance characteristics of the commercial serologic assays currently available have not been established yet (i.e., there are questions around sensitivity, specificity, predictive values, etc.) Some data do indicate good specificity for some serologic tests, with little cross-reactivity to other viruses.

 Under the FDA Emergency Use Authorization (EUA), serologic test kits have been cleared for marketing, yet there is still serious uncertainty on how to interpret these tests. The public health leaders at the CDC have not yet provided guidance on the use of these tests, which is a telling sign that serologic testing is still in need of "clinical validation.''

Until we see results of research studies soon on immune responses to this virus -- whether there is immunity to infection (short- or long-term) and correlates of protection by serologic testing -- the fact remains: it is still too early to implement testing for making clinical or patient management decisions.
 

Irving Nachamkin, DrPH, MPH, D(ABMM), FAAM, FIDSA, is the Director of the William Pepper Laboratory and the Division of Laboratory Medicine at Penn Medicine.

Disclaimer: The views and opinions expressed in this blog column are those of the authors or other attributed individuals and do not necessarily represent the official position of the Department, Penn Medicine, or the University of Pennsylvania. Health information is provided for educational purposes and should not be used as a source of medical advice or diagnosis.