The value of rocket immunoelectrophoresis for C4 activation in the evaluation of patients with angioedema or C1-inhibitor deficiency.

The correct diagnosis and characterization of C1-inhibitor deficiency depends on both clinical observations and laboratory evaluation of complement in plasma. Rocket immunoelectrophoresis for C4d is a sensitive assay for C4 activation in plasma. We have evaluated the value of this assay in identifying patients with C1-inhibitor deficiency. C4 activation was assessed in the plasmas of 15 patients with hereditary angioedema, five patients with variant form of hereditary angioedema, and four patients with acquired C1-inhibitor deficiency. Control groups consisted of 27 patients with chronic idiopathic urticaria and/or angioedema and seven normal volunteers. C4 activation was detected in all 52 plasma samples collected from the 24 patients with C1-inhibitor deficiency. The degree of C4 activation increased during attacks of angioedema and decreased (but remained elevated) during treatment with attenuated androgens. The concentrations of C4, C2, and C1 inhibitor were also measured; however, none of these measurements identified all of the patients with C1-inhibitor deficiency. Thus, we conclude that the measurement of C4 activation is one of the best tests available to evaluate a patient for C1-inhibitor deficiency, and a normal result will exclude the diagnosis of C1-inhibitor deficiency.