Patients were eligible for study if their platelet count fell by more than 50% or to fewer than 100 x 109/L or if they exhibited new thrombosis while receiving heparin.

A strict criterion for study entry was laboratory confirmation of the clinical diagnosis of HIT by the heparin-induced platelet activation (HIPA) test (Greinacher et al., 1991; Eichler et al., 1999) (see Chapter 10).

Clinical outcomes included a composite endpoint (new thrombosis, limb amputation, death) as well as each individual endpoint. Clinical events that occurred between diagnosis and start of treatment with lepirudin were included, as were all clinical events that occurred up to day 14 after stopping lepirudin treatment. Clinical outcomes for lepirudin were compared by Kaplan-Meier time-to-event analysis with a historical control group treated conventionally, beginning at laboratory confirmation of HIT for lepirudin-treated patients and one day after laboratory confirmation for controls.

Laboratory response was defined as (1) the maintenance of an on-treatment aPTT ratio higher than 1.5 in at least 80% of measurements and requiring no more than two dose increases and (2) an increase in the platelet count to more than 30% from the nadir and to more than 100 X109/L by day 10 of lepirudin treatment (thrombocytopenic patients), or maintenance of normal platelet counts on days 3 and 10 (nonthrombocytopenic patients). Patient characteristics are given in Table 3.

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