A sensitive method to assay blood complement C1- inhibitor activity

Clin Chim Acta. 1988 May 31;174(2):121-30. doi: 10.1016/0009-8981(88)90379-8.


Hereditary angioneurotic edema results from deficiency of complement protein C1- inhibitor. Using a new spectrophotometric assay for C1-s esterase activity on the N-alpha-benzoyl-L-arginine ethyl ester, we describe a routinely available method for quantifying low C1- Inhibitor functional activities in EDTA-treated plasma of hereditary angioneurotic edema patients. C1- Inhibitor activity is deduced from the residual esterase activity of C1-s incubated with 20-80 microliters plasma samples. Arbitrary units (volume of sample inhibiting 50% of C1-s activity) were used to express C1- Inhibitor normal activity which was estimated as 22,500 +/- 5,000 (SD) U/l in 45 healthy individuals. The correlation with C1- Inhibitor antigen in these healthy individuals and 89 patients with varying concentrations of C1 Inhibitor ranging from 0.05-1.05 g/l was r = 0.91. Levels down to 2,000 U/l could be estimated. Specific inhibitory activity is an absolute requirement to distinguish between type I and type II hereditary angioneurotic edema.

MeSH terms

  • Complement C1 Inactivator Proteins / blood*
  • Complement C1s / analysis
  • Humans
  • Spectrophotometry, Ultraviolet / methods


  • Complement C1 Inactivator Proteins
  • Complement C1s