Complement component analysis is valuable for differentiating the various types of angioedema. Patients with hereditary angioedema have decreased levels of C1 esterase inhibitor and C4 in the presence of normal amounts of C3 and C1q. Acquired C1 esterase inhibitor deficiency secondary to malignant disease is also manifested by depressed C1 esterase inhibitor and C4, but decreased C1q levels distinguish it from hereditary angioedema. Normal values for these complement components are found in persons with allergic angioedema.
Brasher GW, Starr JC, Hall FF, Spiekerman AM. Complement Component Analysis in AngioedemaDiagnostic Value. Arch Dermatol. 1975;111(9):1140-1142. doi:10.1001/archderm.1975.01630210056003