| Description: |
Heparin-induced thrombocytopenia is a common clinical problem, with 1% to 5% of patients treated developing platelet counts <100 x 109/L. An unpredictable subset of patients whose platelet count falls on heparin therapy will develop heparin-associated thrombosis. Most patients developing this complication have platelet counts <100 x 109/L; however it is important to note that patients with mild thrombocytopenia from heparin or patients on heparin with platelet counts in the normal range have developed heparin-associated thrombosis. The etiology of heparin-induced thrombocytopenia appears to be antibody-mediated and directed against the platelet factor IV- heparin complex. The basis for the heparin-induced aggregation test is that plasma from patients with heparin-induced thrombocytopenia will induce aggregation of normal platelets in the presence of heparin. This test has a high specificity (>90%) but low sensitivity (36% in one study). Therefore, a positive test result strongly supports a diagnosis of heparin-associated thrombocytopenia, but a negative result does not exclude the diagnosis. |
