Applicationof Enzyme Immunoassaysto CoagulationTesting

Enzyme immunoassaysare very useful for the detectionof low concentrationsof coagulationproteinsand pathological markers in plasma. Analytes in the ng/mL range are measur-able with good reproducibility with intra- and interassay CVs of less than 5 % to 10%. “Sandwich ” methods have been developed for von Willebrand factor (plasma concentration about 8.&.g/mL,Factor IX (5 p.g/mL),proteinC (4 g/mL), and Factor X (10 g/mL). However, this technique is only suitable for macromolecules; for low-molecular-mass pep-tides such as fibrinopeptide A a competitive method is used. Normal concentrationsoffibrinopeptideA arebelow 3 ng/mL, with greater values suggesting in vivo generation of throm-bin; thus this test is quite useful in detecting thrombosis. Reagents for both the sandwich and competitive methods are commerciallyavailable and cost effective, and have a longershelf-lifethan those for radioimmunoassays. AddItIonal Keyphrases: “sandwich ” immunoassay thrombosis von Willebrand factor Factor IX. Factor X. protein