NYC health department warns against use of antibody tests to gauge previous infections and immunity

The New York City Department of Health and Mental Hygiene issued guidance to medical providers and advised them not to use antibody testing to determine whether someone has had COVID-19 in the past or whether they have developed immunity to it, the New York Post reported.

Antibody studies are being conducted around the world as public health officials attempt to get a better idea of just how widespread the novel coronavirus is. Results from such studies have shown the actual number of total infections is likely many times more than the confirmed case count.

"Although there is interest in identifying individuals who may be immune to SARS-CoV-2 due to previous infection, significant voids remain in our scientific understanding of the pathophysiology of SARS-CoV-2 which make interpreting serologic assays challenging for clinical and public health practice," read the letter from Demetre C. Daskalakis, the deputy commissioner of the health department's disease control division. "Given the current lack of evidence that detection of SARS-CoV-2 antibody on any serologic test is indicative of durable immunity, it should not be used for that purpose.

"Serologic tests should not be used to diagnose acute or prior SARS-CoV-2 infection, nor should they be used to determine immune status to SARS-CoV-2," the letter continued. "They may produce false negative or false positive results, the consequences of which include providing patients incorrect guidance on preventive interventions like physical distancing or protective equipment."

Daskalakis wrote that antibody tests can't detect current infections, and there is a lag time of a few days before the antibodies show up. That means a negative antibody test doesn't necessarily mean the person isn't currently infected with COVID-19. Additionally, the presence of antibodies from other, more common human coronaviruses may trigger a positive antibody test, even if it's not COVID-19.

A recent serological study in New York indicated that nearly 3 million people in the state may have been infected at some point, including nearly million people in New York City. Gov. Andrew Cuomo (D) announced the results of that study Thursday.