In this issue of CHEST (see page 837), Trehel-Tursis and colleagues1 from France report their 6-year study (ending December 2010) of heparin-induced thrombocytopenia (HIT) occurring in a cardiothoracic surgery ICU. During this time, nearly 6,000 patients entered their ICU: 46% postcardiac surgery, 9% postcarotid endarterectomy, and 45% postthoracic surgery; 101 of 5,949 patients (1.7%) were suspected of possibly having HIT. All patients with suspected HIT were investigated by a polyspecific anti-PF4/heparin enzyme-linked immunosorbent assay (ELISA) that detects IgG, IgA, and IgM class antibodies. In about 90% of patients, additional testing was performed using a functional (platelet activation) assay, either a platelet aggregation test (PAT) or the serotonin release assay (SRA), or both. With few exceptions, patients were considered to have HIT if they tested positive in both the ELISA and one of the functional assays.