Limitations of Functional Monitoring Tests

Results obtained with the aPTT or ECT may be inaccurate in patients whose plasma has a reduced concentration of prothrombin (e.g., severe liver disease, disseminated intravascular coagulation [DIC], treatment with vitamin K antagonists) or in patients with fibrinogen depletion (e.g., post-thrombolysis, hemodilu-tion during CPB) (Lindhoff-Last et al., 2000b; de Denus and Spinier, 2002). This is especially problematic during CPB. In the ECT, this can be overcome by addition of normal plasma 1: 1 to the assay (Koster et al., 2000a).

EIAs measure the plasma concentration of lepirudin independent of pro-thrombin concentration. Plasma concentrations for lepirudin are 0.2-0.4 mg/mL

for thrombosis prophylaxis, and 0.6-1.0 mg/mL for treatment of isolated HIT and for treatment of thrombosis complicating HIT.

The ECA also overcomes the problems associated with monitoring of DTIs by aPTT and ECT, with faster turnaround time than the EIA.

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