Plasma beta-thromboglobulin as a measure of platelet activity. Effect of risk factors and findings in ischemic heart disease and after acute myocardial infarction.

The plasma concentration of beta-thromboglobulin (BTG), a platelet-specific protein released during platelet aggregation, is considered a sensitive marker of in vivo platelet activity. The mean plasma level in 133 asymptomatic individuals was 32.3 +/- 1.1 ng/ml, and there was no difference between those with no risk factors (32.2 +/- 1.2 ng/ml, n = 56), those who smoked (31.8 +/- 1.8 ng/ml, n = 45), those with hyperlipidemia (32.8 +/- 1.7 ng/ml, n = 15), and those exposed to both of these risk factors (34.1 +/- 2.7 ng/ml, n = 17). The mean plasma BTG level in 104 patients with symptomatic ischemic heart disease was significantly elevated (40.9 +/- 1.4 ng/ml, p less than 0.01), but there was considerable overlap with normal levels. Although no difference was found between patients with no risk factors (38.1 +/- 4.0 ng/ml, n = 13) and those with only 1 risk factor (37.0 +/- 1.8 ng/ml, n = 44), patients with 2 or more risk factors ahd a significantly elevated plasma BTG level (45.2 +/- 2.2 ng/nl, n = 47, p less than 0.01). It is concluded that risk factors themselves do not increase platelet activity, but that patients with vascular disease have activated platelets that may contribute to the progression of the disease. Plasma BTG was also measured serially for 10 days in 29 patients after hospitalization with acute ischemic cardiac pain. Although the median plasma level was elevated above normal there were no acute changes in plasma BTG after either acute infarction (n = 22) or acute ischemia (n = 7), except in 2 patients in whom pericardial friction rubs developed. Thus, measurement of systemic plasma BTG did not detect platelet involvement in acute coronary occlusion or acute ischemia.