BETA-THROMBOGLOBULIN IN PLASMA - FALSE HIGH VALUES CAUSED BY PLATELET ENRICHMENT OF THE TOP LAYER OF PLASMA DURING CENTRIFUGATION

β-thromboglobulin was measured and platelets were counted separately from the top and middle layers of plasma prepared by double centrifugation. A variable high number of platelets was found in the top layer and a linear correlation existed between the platelet count and the β-thromboglobulin level. In the middle layer both the platelet count and the β-thromboglobulin value was constantly low. More platelets were found in the top layer after fasting than after fatty meal. Slight disturbance of the sample caused sedimentation of part of the top layer with consequent contamination of the middle layer by platelets. Enrichment of the top layer with platelets could be diminished by incubating the sample with ristocetin. Instead of using the top part of plasma for β-thromboglobulin assay, a carefully taken middle layer sample is recommended if high g-forces have been used. © 1979.