Platelet markers of thromboembolic disease.

Platelets may be useful as markers of thromboembolic disease. When labeled with indium 111 they allow external imaging of localized clots. Indium 111 is much superior to chromium 51 for this procedure. Detection of circulating platelet aggregates also appears to be a simple means of determining the presence of thromboembolic disorders. In response to injury or involvement in clotting, platelets release several unique proteins not normally found in the plasma. Therefore, elevated levels of these proteins suggest the presence of such damage. Platelet factor 4 and beta-thromboglobulin are the most widely studied of these proteins, and both can be quantitated by radioimmunoassay. Such assays are now commercially available. Elevated levels have been demonstrated in such diverse disorders as deep venous thrombosis, atherosclerosis and diabetes. However, blood must be drawn with great care to avoid in vitro damage to platelets and false elevation of these markers. All of these procedures are promising at present, but their precise role and value await further study.