HIT was assumed to be the cause of thrombocytopenia beyond day 5 of ICU treatment, because high-titer antiplatelet factor 4 immunoglobulin G antibodies were detectable by enzyme-immunoassay and the heparin-induced activation assay was strongly positive at day 6 of heparin treatment. However, the moderate increase of the platelet count after switching to nonheparins indicated that HIT was probably not the only cause of thrombocytopenia. EIA, enzyme-immunoassay; HIPA, heparin-induced platelet activation assay; OD, optical density.