An immunodiffusion assay for detecting C1 inhibitor function in human serum was described recently by Ziccardi and Cooper. In our present study, the applicability of this assay for C1 inhibitor deficiency or C1 inhibitor dysfunction was evaluated. Of the 39 patients evaluated, all eight patients with the common (C1 inhibitor deficiency) form of hereditary angioedema and all three patients with the variant (dysfunctional C1 inhibitor) form of hereditary angioedema were identified correctly. Treatment of patients with hereditary angioedema with stanozolol or danocrine increased their serum C1 inhibitor concentrations and normalized the immunodiffusion assay for C1 inhibitor function. In addition, the assay allowed the correct identification of three patients with the acquired form of C1 inhibitor deficiency, because the sera of these patients exhibited a distinctive pattern. The 25 samples from patients (chronic angioedema, chronic urticaria, or hypocomplementemic vasculitis) without C1 inhibitor deficiency had normal assays.
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