Heparin-induced thrombocytopenia: a prospective study of 142 patients.

In a prospective study of 142 patients receiving intravenous heparin of bovine lung origin, thrombocytopenia developed in nine (6%) patients. In the group of 70 patients with a history of prior heparin therapy, seven (10%) had thrombocytopenia. By contrast, only 2 (3%) of 72 patients with no history of previous heparin treatment had thrombocytopenia, a statistically insignificant difference (p less than 0.5). In this group 58 patients received heparin for less than 10 days, and none of them had thrombocytopenia. Of the remaining 14 patients who were given heparin longer than 10 days, two patients (14%) had thrombocytopenia. This difference was statistically significant (p less than 0.01). Monitoring the platelet count detects the disorder early and prompt cessation of heparin prevents serious complications. All patients undergoing heparin therapy should have determination of pretreatment platelet count. In patients with a history of previous heparin therapy, thrombocytopenia may develop even with short duration of heparin treatment, and hence platelet counts should be monitored throughout the duration of treatment. The platelet count of patients who have no history of previous treatment with heparin should be monitored if heparin is continued for more than 7 days.