Factor XII (aka Hageman Factor) is a single-chain, 615 amino acid glycoprotein zymogen. Factor XII is activated by kallikrein. Factor XIIa converts prekallikrein to kallikrein during the intrinsic pathway of the coagulation cascade. Although Factor XII is not thought to play an essential role in normal hemostasis, lack of Factor XII in a mouse model resulted in a severe defect in thrombus formation. The sensitive quantitative measurement of total rat Factor XII antigen in plasma samples is easily performed with this 96 well strip format ELISA kit. Factor XII and XIIa will be detected by the assay. The concentration of Factor XII in normal human plasma ranges from 15-47 ug/ml. Normal values of Factor XII in rat plasma have not been conclusively determined but are believed to be similar to human plasma based on in-house testing. The assay measures total rat Factor XII in the 0.01-10 ng/ml range. Samples giving rat Factor XII levels above 10 ng/ml should be diluted in blocking buffer before use. A 1:10,000 to 1:100,000 dilution for plasma is suggested for best results. Rat Factor XII will bind to the capture antibody coated on the microtiter plate. After appropriate washing steps, biotin labeled anti-rat Factor XII primary antibody binds to the captured protein. Excess primary antibody is washed away and bound antibody is reacted with streptavidin conjugated to HRP. Following an additional washing step, TMB substrate is used for color development at 450nm. Color development is proportional to the concentration of Factor XII in the samples. A standard calibration curve is prepared using dilutions of purified Factor XII and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.