Plasminogen activator inhibitor type 1 deficiency

Summary. Plasminogen activator inhibitor type 1 (PAI‐1) is an important component of the coagulation system that down‐regulates fibrinolysis in the circulation. Reduced PAI‐1 levels may result in increased fibrinolysis and an associated bleeding diathesis. Clear documentation of PAI‐1 deficiency as a cause of a bleeding disorder has been rare. PAI‐1 was initially identified in the 1980s, and the first reported case of PAI‐1 deficiency appeared in 1989. Several reports followed, although only two identified an underlying genetic defect. These reports of PAI‐1 deficiency suggest that affected individuals exhibit mild to moderate bleeding symptoms, including epistaxis, menorrhagia, and delayed bleeding after trauma or surgical procedures. Affected individuals rarely exhibit spontaneous bleeding events commonly seen in other procoagulant deficiencies. The majority of bleeding events are controlled with antifibrinolytic agents, such as tranexamic acid and ε‐aminocaproic acid. A major issue that contributes to difficulty in establishing an accurate diagnosis of PAI‐1 deficiency is that the activity assay is accurate in detection of elevated levels but not at the lowest range. Reported normal ranges begin at zero, thereby making a deficiency state because of a dysproteinaemia difficult to distinguish from that of a normal unaffected individual. Although the antigen assay may be helpful in some circumstances, it assists only with complete quantitative disorders. Because of lack of standardized commercially available PAI‐1 activity assay sensitive in the lowest range, the true prevalence of this rare condition has not been established.