Releasable tissue plasminogen activator (t-PA) and the fast inhibitor of t-PA were measured in 18 controls and a pedigree with venous thrombosis. The functional assay was performed by a technique that destroys the t-PA inhibitor when blood is drawn. It was found that activator and inhibitor levels varied widely in the control group. One patient demonstrated inhibitor levels, on two different occasions, of 2.82 and 3.54 IU of t-PA per milliliter of plasma, as compared with a releasable activator level of 1.87 IU/mL. The t-PA antigen levels of this patient and the remainder of the pedigree were essentially normal for all seven subjects. Thus, it is suggested that the previously reported fibrinolytic disorder in this pedigree represents an imbalance between activator and inhibitor levels rather than an actual deficiency of t-PA.
(Arch Intern Med 1986;146:188-191)