High molecular weight kininogen (HK, aka Fitzgerald Factor) is the single chain 626 amino acid 120kDa glycoprotein precursor of the vasoactive peptide bradykinin. Kininogen is an important cofactor for the activation of zymogens prekallikrein, Factor XII, and Factor XI in the contact activation or intrinsic coagulation pathway. Additionally kininogen is a major inhibitor of systemic cysteine proteinases such cathepsins, calpain and papain. The sensitive quantitative measurement of total human kininogen antigen in plasma and serum samples is easily performed with this 96 well strip format ELISA kit. The concentration of prekallirein in normal human plasma is 65-115 ug/ml with an average concentration of 83 ug/ml. The assay measures human kininogen in the 0.1-100 ng/ml range. Samples giving human kininogen levels above 100 ug/ml should be diluted in blocking buffer before use. A 1:10,000-1:50,000 dilution for plasma is suggested for best results. Human kininogen will bind to the monoclonal capture antibody coated on the microtiter plate. After appropriate washing steps, biotinylated anti-human kininogen 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 kininogen in the samples. A standard calibration curve is prepared using dilutions of purified kininogen and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.