ABSTRACT
Thrombocytopenia occurs commonly during heparin therapy, usually as a transient fall in platelet count 1-3 days after initiation of treatment. In most patients, this is of no clinical significance and platelet levels return to normal within 3 days, with or without discontinuing the heparin administration. In contrast, a relatively small group of patients develop thrombocytopenia, with a characteristic delay that is usually 5-10 days after starting heparin therapy, although some patients recently exposed to heparin develop an abrupt onset of thrombocytopenia. Paradoxically, many of these patients experience venous or arterial thromboembolism (see Chapter 2). To early investigators, this profile of a delay in onset of thrombocytopenia, as well as abrupt recurrence on rechallenge, suggested an immune pathogenesis (see Chapter 1).
