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Laboratory Techniques in Fibrinolysis Testing
The purpose of this chapter is to provide an overview of laboratory techniques involved in fibrinolysis testing. Chapter 145 provides a general introduction to fibrinolytic testing and common fibrinolytic disorders ( Fig. 146.1 ).
The fibrinolytic pathway in coagulation.
α 2 AP , α 2 antiplasmin; α 2 MG , α 2 macroglobulin; ECM , extracellular matrix; FDP , fibrin degradation products; HRG , histadine-rich glycoprotein; MMP , matrix metalloproteinases; PAI-1 , plasminogen activator inhibitor-1; TAFI , thrombin activatable thrombinolysis inhibitor; TPA , tissue plasminogen activator.
From Abshire, T. (2009). Laboratory techniques in fibrinolysis testing. In C. D. Hillyer, B. H. Shaz, J. C. Zimring, & T. C. Abshire (Eds.), Transfusion medicine and hemostasis: clinical and laboratory aspects (pp. 671–676). Elsevier.
Screening Tests
Euglobulin Lysis Time
The euglobulin lysis time (ELT) is a historical screening test for hyperfibrinolysis. Newer, more specific tests for individual fibrinolytic factors and more rapid tests, such as thromboelastometry, have supplanted ELT. To measure ELT, the euglobulin fraction of the plasma-containing plasminogen, plasminogen activators, and fibrinogen is acid-precipitated then clotted with thrombin. Time to clot disappearance is determined. A positive test is premature clot disappearance in 60–120 minutes, suggesting increased fibrinolysis, although the specific cause of the excessive fibrinolysis is not determined by this methodology.
Thromboelastometry/Thromboelastography
Thromboelastometry (and related thromboelastography) has largely replaced ELT as a screening test for hyperfibrinolysis in acute settings. Whole blood or plasma is clotted. Fibrinolysis is measured as the difference between the maximum viscoelasticity achieved after the clot formation and the clot viscoelasticity at 30 and 60 minutes after the maximum. Either percent clot lysis or rate of clot lysis can be measured. Proof of fibrinolytic activity can be shown by adding a fibrinolytic inhibitor such as aprotinin. This methodology is sensitive to moderate to severe increases in fibrinolytic activity but not to mild abnormalities such as PAI-1 or antiplasmin deficiency or modest increases in tissue plasminogen activator (t-PA) activity. When fibrinolysis is obvious on thromboelastometry, clinical bleeding is often evident.
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