DEFINITION

Prekallikrein activator (PKA), also known as Factor XIIa, activates prekallikrein to kallikrein. Activated kallikrein cleaves kininogens into kinins (e.g., bradykinin) that can result in a loss of blood pressure. PKA is assayed by its ability to activate prekallikrein, which once activated cleaves a synthetic peptide substrate and releases a chromophore that can be measured spectrophotometrically. The amount of PKA is determined by comparison with reference standard material. The procedure presented in this chapter traditionally has been used to determine the amount of PKA in human plasma derivatives such as albumin and immunoglobulin preparations.