title: A novel clotting assay for quantitation of plasma prothrombin (factor II) using Echis multisquamatus venom.
abstract: Measuring plasma prothrombin activity seems useful for evaluating thrombotic risk and managing oral anticoagulant therapy as an adjunct to the international normalized ratio. Therefore, we designed a new plasma prothrombin assay based on the ability of Echis multisquamatus venom to activate prothrombin with only calcium as a cofactor. In this assay, 1 part of undiluted citrated plasma is added to 5 parts of a venom reagent and the clotting time is measured. The assay's advantages are that dilution of the test plasma is required only when prothrombin activity exceeds 100%, a single standard curve can be used over months for a given batch of stock reagent, and barium-adsorbed plasma is used for dilution of test plasma and construction of the standard curve, thus eliminating the need for prothrombin-deficient plasma. However, one should be aware of the following: (1) test samples must contain at least 200 mg/dL fibrinogen; and (2) when prothrombin concentrations were below 50%, the venom-based assay often gave values up to 10% higher than the thromboplastin-based assay. Values obtained in 262 plasma samples tested with the venom-based assay and with a thromboplastin-based prothrombin assay correlated well (r2 = 0.93).
authors.affiliation: Department of Pathology, University of California, San Diego 92093-0612, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Petrovan
authors.forename: S I
authors.initials: SI
authors.lastname: Rapaport
authors.forename: D T
authors.initials: DT
authors.lastname: Le
mesh_terms: D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects*; D001780:Blood Coagulation Tests / Q000379:methods*; D002118:Calcium / Q000097:blood; D005069:Evaluation Studies as Topic; D006801:Humans; D010314:Partial Thromboplastin Time; D011516:Prothrombin / Q000032:analysis*; D012016:Reference Values; D015203:Reproducibility of Results; D014757:Viper Venoms / Q000494:pharmacology*; D017819:Viperidae
chemical_list: D014757:Viper Venoms; D011516:Prothrombin; D002118:Calcium