Platelet factor 4 plasma levels at rest and after exercise in patients with recent myocardial infarction

Plasma levels of platelet factor 4 (PF 4) were determined in 30 patients with recent acute myocardial infarction. Comparisons were made with the levels in 26 age-matched controls. In another 15 patients, also with recent myocardial infarction, PF 4 plasma levels were determined before and immediately after a standardized exercise stress test. At rest, none of the patients had elevated PF 4 levels. Only one patient demonstrated an increase after exercise. These findings are in conflict with some recent reports. The importance of age-matched controls, the hazard of in vitro platelet activation and the possible effect of beta-blocking and calcium-antagonistic drugs on PF 4 plasma levels is discussed below.