CLINICAL USEFULNESS OF TESTING FOR A HEPARIN-DEPENDENT PLATELET-AGGREGATING FACTOR IN PATIENTS WITH SUSPECTED HEPARIN-ASSOCIATED THROMBOCYTOPENIA

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 103  (4) , 606-612
Abstract
It is important to confirm the diagnosis of heparin-associated thrombocytopenia, because discontinuation of heparin requires the institution of other antithrombotic therapy. Reports describing a heparin-dependent platelet-aggregating factor in the serum of patients with heparin-associated thrombocytopenia suggest the potential for a specific diagnostic test. No study has evaluated the diagnostic usefulness of testing for this factor. The sera from 14 patients with heparin-associated thrombocytopenia, 14 nonthrombocytopenic controls given heparin, 16 patients with consumptive thrombocytopenic disorders not associated with heparin and 13 healthy laboratory personnel were tested. Coded serum samples plus varying concentrations of heparin (final concentration 0.01, 0.1, 1.0 and 5 U/ml) plus platelets from healthy individuals were incubated together and aggregation was measured. Positive results (> 20% aggregation) occurred in 5 of 14 patients with heparin-associated thrombocytopenia, 0 of 16 consumptive thrombocytopenic controls not given heparin therapy, 1 of 14 nonthrombocytopenic controls given heparin and 1 of 13 healthy controls, giving a sensitivity of 36% and specificities of 100, 93 and 92%, respectively. No unique clinical or laboratory feature distinguished those patients with heparin-associated thrombocytopenia with positive aggregation results from those patients with heparin-associated thrombocytopenia with negative results. Fourteen of the 16 patients (86%) with heparin-associated thrombocytopenia had elevated levels of platelet-associated IgG; however, the test was also positive in 67% of the 16 patients with other consumptive (and probably immune) thrombocytopenic disorders not associated with heparin administration. Testing for the presence of a heparin-dependent platelet-aggregating factor in a patient with suspected heparin-associated thrombocytopenia may help in clinical decision making. A positive result supports the diagnosis, but a negative result does not exclude it. Efforts should be directed at increasing the sensitivity of this test. It is possible that a more sensitive end point, such as platelet serotonin release, would increase the diagnostic sensitivity and hence clinical applicability of the test.