COVID‐19 patients often show high‐titer non‐platelet‐activating anti‐PF4/heparin IgG antibodies

Abstract

Heparin‐induced thrombocytopenia (HIT) is a severe adverse reaction to heparin caused by heparin‐dependent, platelet‐activating anti‐platelet factor 4 (PF4)/heparin antibodies. Heparin is a cornerstone of treatment in critically ill COVID‐19 patients. HIT antibodies can be detected by antigen tests and functional tests. Often strong reactivity in the antigen test is used as a surrogate marker for the presence of clinically relevant, platelet‐activating antibodies. We observed an unexpectedly high percentage of COVID‐19 patients, clinically suspected to have HIT, with high titer anti‐PF4/heparin antibodies, but a negative functional test.