In our surgical intensive care unit (ICU), we recently observed two cases of HIT responsible for repeated hemofiltration-filter clotting in the absence of typical thrombocytopenia [8] and we then systematically measured the plasma anti-PF4/heparin antibody concentration in all patients with repeated hemofiltration-filter clotting during CVVH, with no obvious cause. Here, PF4 is linked to Thrombocytopenia.