[The value of platelet function tests].

Abstract

Platelet function tests are used to detect patients with abnormal platelet function, which may be inborn or acquired or to detect increased platelet activation which may be accompanied by an increased risk of thrombosis. Platelet function tests are also used to monitor platelet function inhibitors as aspirin, clopidogrel or platelet membrane glycoprotein IIb/IIIa-inhibitors. Incorrect blood sampling is a major source of error in measuring platelet function. Global tests besides platelet count and bleeding time are thrombelastography, the platelet function analyzer (PFA) and possibly in the future the new Impact-system. Specific tests measure platelet spreading and adhesion to defined surfaces. In a series of methods platelets are counted before and after passage of a filter. Some of these tests are partially standardized. The most frequently measured platelet function is aggregation induced by ADP, collagen or other substances as first described by Gustav Born. Some newer methods to perform aggregometry are described. Platelet activation can be detected by measuring spontaneous aggregation as in the PAT-test. Prospective trials with this test have shown that enhanced spontaneous aggregation is a risk factor for new vascular occlusions in diabetics and for myocardial infarctions in healthy individuals. The Wu and Hoak-test and the measurement of released platelet factor 4 or betaglobulin are of limited value. Flow cytometric methods are frequently used to measure platelet activation markers as CD 62 and others. Platelet induced thrombin generation is an interesting function to measure drug effects. None of the presently available platelet function tests is well standardized, so there is much room for improvement.