ABSTRACT : Whereas some 30% to 50% of patients admitted to the intensive care unit develop thrombocytopenia during their stay, the incidence of heparin-induced thrombocytopenia (HIT) remains low, at around 0.3% to 0.5%. Lasocki and colleagues prospectively tested patients with premature clotting of the hemofiltration circuit for HIT, and reported a 25% incidence of HIT, particularly if the circuit clotted within 6 hours. By switching the anticoagulant from heparin to danaparoid, the hemofiltration circuit survival and urea clearances improved. HIT should therefore be clinically suspected if extracorporeal circuits clot repeatedly.