Abstract
Plasma C1 inhibitor (C1-INH) was determined in 64 patients with different malignant diseases and in 58 healthy persons. C1-INH antigen concentration was measured by radial immunodiffusion (RID), whereas its functional activity was assayed with chromogenic substrate. Within-run and day-to-day precision of both methods were good, with CVs ranging from 3·6 to 5·4%. Plasma C1-INH antigen concentrations were significantly higher in the patients than in healthy controls (P = 4·0 × 10−3), as were their C1-INH functional activities (P = 3·5 × 10−3). C1-INH activities obtained in the patient plasma samples were in correlation with their antigen concentrations (r = 0·914), showing that C1-INH synthesized in malignant disease was functional. However, the specific activity of the C1-INH (functional activity/antigen concentration ratio) was significantly lower in the patient group as compared with the controls (P = 2·1 × 10−6), indicating partial inactivation of plasma C1-INH in malignant diseases. The C1-INH specific activity in patients was inversely proportional to its antigen concentration.