A formula for correcting for the in vitro release of platelet beta-thromboglobulin.

The interpretation of platelet beta-thromboglobulin (BTG) and platelet factor 4 (PF4) levels as indicators of in vivo platelet activation is complicated by the artefactual release of these proteins in vitro. A formula was devised to correct for in vitro platelet activation and release of BTG. Blood was collected from normal volunteers by an ideal method and BTG and PF4 levels determined by radioimmunoassay; these were the reference values. Blood from normal volunteers was activated in vitro by standing at room temperature. The BTG and PF4 released was measured at different time intervals. The relationship between BTG and PF4 released was measured at different time intervals. The relationship between BTG and PF4 was measured mathematically best described by a second degree polynomial function. The true plasma BTG value was then calculated by correcting for in vitro release by the general formula: BTG corrected = BTG measured - BtG for PF4 measured + BtG for PF4 reference The validity of the correction formula was tested in 10 normal subjects and in patients with either recent myocardial infarction(n = 10), familial hypercholesterolaemia(n = 10) or arterial prostheses(n = 14). Correction was adequate in normal subjects if the plasma BTG levels did not exceed 260ng/ml. In patients with a thrombotic tendency, the formula overcorrected for in vitro release. This could be ascribed to increased in vivo PF4 levels in these patients, especially those with prostheses. The reference values for PF4 in these patients, and especially those with vascular prostheses, were also higher than normal. The PF4 measured in their plasma thus reflects both in vivo and in vitro released protein. The hypothesis on which the correction formula was based, is therefore not always applicable. It may be possible to improve the correction by establishing formulae for specific disease groups.