Platelet aggregation, stroke, and transient ischemic attack in middle-aged and elderly patients.

Platelet aggregation was studied with optical density methods in a group of 39 patients with stroke or transient ischemic attacks (TIA) and in age, sex, and race-matched controls. The patients were divided at age 60 into young stroke patients and young controls (18 pairs) and old stroke patients and old controls (21 pairs). A semiquantitative measure of the threshold of phase II of platelet aggregation and distinct of disaggregation 3 minutes after peak aggregation were used as an index of platelet aggregability. Aggregability was significantly greater in young stroke patients than in young controls. Aggregability was similar in old stroke patients and old controls. Both old stroke patients and old controls were hyperaggregable compared with young controls, indicating that aggregability rises with age. This suggests that platelet aggregability is significant risk factor for stroke but is relatively more important in the younger than in the older stroke patient.