Repeat heparin exposure in the presence of a positive baseline EIA (patient 20). (A) Previous episode of HIT (2010). (B) Platelet counts after UFH rechallenge (2011) for urgent cardiac surgery (severe mitral regurgitation). (C) Anti-PF4/heparin antibodies and SRA results at the time of the previous episode of HIT and (D) at heparin rechallenge approximately 5 weeks after the first negative SRA. The data illustrate an uneventful UFH reexposure despite a moderate positive EIA-IgG (1.98 OD units)—with a negative SRA—at time of heparin rechallenge, which was accompanied by increase in IgG levels to almost 2.50 OD units as well as weak IgA seroconversion. The shaded area indicates a platelet count range expected for a postcardiac surgery patient population.2 Pos, positive; SD, standard deviation.
