Prekallikrein is the glycosylated single chain zymogen precursor of the plasma serine protease kallikrein. Plasma prekallikrein circulates with kininogen and is activated by Factor XIIa in the intrinsic coagulation pathway. Kallikrein activates plasminogen in fibrinolysis and cleaves kininogen in the bradykinin system of vasodilation. Prekallikrein deficiency is rare and causes increased activated partial thromboplastin time. Elevated plasma prekallikrein is associated with diabetes and cardiovascular disease. The sensitive quantitative measurement of total human prekallikrein antigen in plasma samples is easily performed with this 96 well strip format ELISA kit. Kallikrein will be detected by the assay. The concentration of prekallirein in normal human plasma is 15-55 ug/ml. The assay measures human prekallikrein in the 0.02-10 ug/ml range. Samples giving human prekallikrein levels above 10 ug/ml should be diluted in blocking buffer before use. Normal human plasma should be applied directly to the plate or at a 1:5 dilution for best results. Human prekallikrein will bind to the capture antibody coated on the microtiter plate. After appropriate washing steps, anti-human prekallikrein primary antibody binds to the captured protein. Excess primary antibody is washed away and bound antibody is reacted with the secondary antibody 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 prekallikrein in the samples. A standard calibration curve is prepared using dilutions of purified prekallikrein and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.