Factor XII assay with the chromogenic substrate chromozym PK.

A chromogenic assay for the determination of factor XII using the chromogenic substrate Chromozym PK was evaluated. The assay was linear in the range 10 U/l to more than 200 U/l. Using the assay, the normal range of factor XII (50 healthy volunteers at random) was 136 U/l +/- 27 U/l. Kallikrein-inhibiting concentrations of aprotinin did not influence factor XII. Comparison of the chromogenic with the clotting assay resulted in a correlation coefficient of r = 0.831 (p-value less than 0.001). In patients with deep vein thrombosis, factor XII level was found to be reduced to about 60% of normal activity.