Factor XI is a disulfide linked two-chain glycoprotein zymogen and is the precursor of the coagulation enzyme Factor XIa. Factor XI consists of two identical monomers and circulates in plasma in complex with kininogen. Factor XI is activated by Factor XIIa and converts Factor IX to Factor IXa during the intrinsic pathway of the coagulation cascade. The sensitive quantitative measurement of total human Factor XI antigen in plasma samples is easily performed with this 96 well strip format ELISA kit. Factor XI and XIa will be detected by the assay. The concentration of Factor XI in normal human plasma ranges from 3-6 ug/ml. The assay measures total human Factor XI in the 0.2-100 ng/ml range. Samples giving human Factor XI levels above 100 ng/ml should be diluted in blocking buffer before use. A 1:1,000 dilution for plasma is suggested for best results. Human Factor XI will bind to the capture antibody coated on the microtiter plate. After appropriate washing steps, peroxidase labeled anti-human Factor XI primary antibody binds to the captured protein. Excess antibody is washed away and TMB substrate is used for color development at 450nm. Color development is proportional to the concentration of Factor XI in the samples. A standard calibration curve is prepared using dilutions of purified Factor XI and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.

The Human Factor XI standard provided in this kit is calibrated against the WHO International Standard for Human Plasma Factor XI (NIBSC Code 04/102).