A rapid method for functional determination of C1 esterase inhibitor in plasma.

A functional determination of C1 esterase inhibitor (C1 INH) can be easily performed with an amidolytic assay by monitoring the inactivation of plasma kallikrein. In patients with urticaria as well as in healthy donors kallikrein inactivation, determined as the ratio of kallikrein activity at t60/t15, was found to be 0.47 +/- 0.06; in patients with hereditary angioneurotic edema (HANE). However, it amounted to 0.80 +/- 0.06. There was a good correlation between the inactivation rate of kallikrein and the protein levels of C1 INH (r = -0.93, p less than 0.001). In patients with HANE, levels of plasma kallikrein were slightly decreased (mean = 0.37 +/- 0.11 U/ml, normal mean = 0.47 +/- 0.09 U/ml), but still sufficient for monitoring kallikrein inactivation. In the case of one patient with functionally inactive C1 INH protein, the inactivation of kallikrein was impaired as in the conventional form of the disease.