The platelet and plasma pools of plasminogen activator inhibitor (PAI-1) vary independently in disease.

The relative importance and behaviour of plasma and platelet plasminogen activator inhibitor (PAI-1) in disease has not hitherto been examined. In this study the concentration of PAI-1 in the plasma and platelets of patients with a variety of disorders was examined using a specific ELISA and a functional assay. Mean plasma PAI-1 was elevated in groups of patients with diabetes mellitus, hypertension, alcoholic cirrhosis, angina and myocardial infarction. Plasma PAI-1 was raised in the post-operative phase and the PAI-1 released after surgery was not derived from platelets. In all groups PAI-1 in the platelet pool reflected the platelet count, except in type II diabetes mellitus and chronic renal failure, where a reduced quantity of PAI-1 antigen per platelet was found. In severe chronic renal failure, abnormal platelets and diminished platelet PAI-1 may contribute to the haemorrhagic tendency sometimes seen in this disorder. Plasma PAI-1 represents a larger proportion of total circulating PAI-1 in disease than it does in healthy individuals; PAI-1 per platelet is abnormal only in a minority of disorders. Plasma and platelet pools of PAI-1 vary independently in disease and both merit consideration in evaluating the importance, if any, of PAI-1 in thrombosis or haemorrhage.