The role of platelets in the coagulopathy of heatstroke a study of platelet aggregation in heatstroke patients during the Makkah pilgrimage (Haj) to

Platelet aggregation was undertaken in platelet rich plasma in 34 heat-stroke patients during the Muslim pilgrimage (Haj) to Makkah; 18 were males and 16 were females; their ages ranged from 36 to 80 years (mean SD = 58 10). Platelet aggregability, on arrival at the Heatstroke Centres, was markedly inhibited in response to adrenaline, collagen, arachidonic acid and ristocetin but not to ADP. Responses to decreasing ADP doses (20.0, 2.0, 1.0 and 0.5 micromol/l) showed hyperaggregability in 12 patients, inhibited responses in 16 and normal responses in 6 patients. Aggregation responses were not significantly different when comparing patients with bleeding manifestations ( n = 10), with those without bleeding ( n = 24). Haemostatic parameters including plasma fibrinogen, ATIII and platelet count, were markedly reduced in the two patient groups who showed hyperaggrebable and depressed aggregation responses, but not in those with normal responses. These results lead us to conclude that: (1) platelet activation is a frequent feature of heatstroke; (2) in heatstroke altered aggregation responses, whether hyperaggregable or depressed, occur simultaneously with a consumption coagulopathy.