Platelet hyperaggregation and increased plasma level of Von Willebrand factor in diabetics with retinopathy.

In 18 insulin-dependent diabetics (6 without retinopathy, 6 with proliferative retinopathy and 6 with proliferative retinopathy treated by hypophysectomy) matched for age and duration of diabetics, in vitro haemostasis was studied using ADP induced platelet aggregation, ristocetin induced platelet aggregation which allows von Willebrand factor (VIII VWF) assay, and determination of antihemophilic factor procoagulant activity (VII AHF). Using gel filtration-isolated platelets, the ADP induced hyperaggregation previously reported in diabetics with severe retinopathy untreated by hypophysectomy appeared to be related to a platelet and not a plasma factor; the normal results of thrombin induced aggregation suggests that the presumed abnormal platelet factor is related to the platelet plasma membrane. High level of plasma VII VWF was observed in diabetics with proliferative retinopathy while the VII AHF level was within normal limits.