If C4 is normal or low and C1-INH antigenic protein normal but clinical suspicion is strong, HAE is NOT ruled out and C1-INH functional assay should be obtained (in a laboratory skilled in functional C1-INH assay with careful sample drawing, handling, shipping, and interpreting results) [8,18,19,28,29,34]. The gene discussed is C4A; the disease is hereditary angioedema.