Alpha-2-Antiplasmin Activity (AP)
Alpha-2-antiplasmin (AP) is the natural inhibitor of the fibrinolytic enzyme plasmin. It is a single-chain glycoprotein which plays a significant role in the specific inhibition of fibrinolysis. The role of AP is threefold:
Rapid inactivation of plasmin proteolytic activity occurs through a two-step process in which AP initially forms a reversible complex with plasmin. This subsequently followed by the formation of a covalent, enzymatically inactive, complex with plasmin's catalytic site.
AP interferes with the binding of plasminogen to fibrin, slowing plasminogen activation by fibrin-bound plasminogen activator and delaying the initiation of fibrinolysis.
Covalent cross-linking of AP to the alpha-chains of fibrin, which is mediated by factor XIIIa, protects crosslinked fibrin clots from plasmin degradation and stabilizes the fibrin clot against fibrinolysis. Failure to protect the fibrin clot from rapid dissolution before healing is complete results in a bleeding tendency.
In the Hemostasis and Thrombosis Laboratory, antiplasmin is measured in a chromogenic assay. The patient's plasma (as a source of antiplasmin) is incubated with purified human plasmin. Residual, non-inhibited plasmin is then measured with a specific chromogenic substrate.
The normal range is 80 - 120%
Acquired decreases in plasma antiplasmin may be found in hepatic insufficiency, treatment with thrombolytic drugs and disseminated intravascular coagulation. Congenital deficiency of antiplasmin has been described and is a relatively rare cause of a bleeding disorder.
