Antiplasmin Deficiency

At a Glance

Antiplasmin is the natural inhibitor of the proteolytic enzyme plasmin, which is generated from the activation of plasminogen. In the absence of antiplasmin, the proteolytic enzyme plasmin excessively degrades fibrin clots, while it also degrades proteins on the platelet surface and in the circulation, including the coagulation factors. It is for this reason that a deficiency of antiplasmin results in bleeding.

The congenital form of antiplasmin deficiency is a rare entity that results in bleeding. The possibility of antiplasmin deficiency enters the differential diagnosis in patients who have an apparent lifelong bleeding disorder but have normal values for the prothrombin time (PT), partial thromboplastin time (PTT), platelet count, platelet function studies, von Willebrand studies, and all other coagulation tests that might be altered in patients with bleeding disorders.

Factor XIII deficiency, like antiplasmin deficiency, should also be considered in this situation, because neither of these deficiencies is associated with other coagulation test abnormalities. An acquired antiplasmin deficiency can occur with continued activation of plasminogen to plasmin. This results in the formation of plasmin-antiplasmin complexes, which are cleared, leading to a reduction in the amount of circulating antiplasmin.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

When considering a diagnosis of congenital antiplasmin deficiency, a test for antiplasmin can be performed to establish the presence of the deficiency. Because it is a rare disorder, a repeat study to confirm the deficiency is essential. It is also important to measure antiplasmin in the absence of fibrinolytic agents, which creates an acquired antiplasmin deficiency by generating plasmin to which antiplasmin will bind.

In patients who have been treated for long periods of time with thrombolytic therapy, there may be interest in understanding the extent of the acquired antiplasmin deficiency. In those situations, measurements of the antiplasmin should occur within minutes to hours after treatment with the thrombolytic therapy to determine the extent of the deficiency created by the therapy. The clinical significance of an antiplasmin deficiency in this setting is uncertain.

What Lab Results Are Absolutely Confirmatory?

A consistently low antiplasmin level in the absence of fibrinolytic therapy is confirmatory for congenital antiplasmin deficiency.