Factor V (aka proaccelerin or labile factor) is a 2224 amino acid single chain glycoprotein. Factor V is activated to Factor Va by thrombin. Factor Va binds to Factor Xa and acts as a cofactor in accelerating the activation of prothrombin to thrombin. A genetic Factor V R506Q mutation has been shown to result in a resistance to activated protein C leading to venous thrombosis. The sensitive quantitative measurement of total human Factor V antigen in plasma samples is easily performed with this 96 well strip format ELISA kit. Factor V and Va will be detected by the assay. The concentration of Factor V in normal human plasma ranges from 4-14 ug/ml. The assay measures total human Factor V in the 0.938-60 ng/ml range. Samples giving human Factor V levels above 60 ng/ml should be diluted in blocking buffer before use. A 1:800 dilution for plasma is suggested for best results. Human Factor V will bind to the capture antibody coated on the microtiter plate. After appropriate washing steps, biotin labeled anti-human Factor V primary antibody binds to the captured protein. Excess primary antibody is washed away and bound antibody is reacted with peroxidase conjugated streptavidin. Following an additional washing step, TMB substrate is used for color development at 450nm. Color development is proportional to the concentration of Factor V in the samples. A standard calibration curve is prepared using dilutions of purified Factor V and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.