Acquired Angioedema Due to C1 Inhibitor Deficiency Workup

Updated: May 20, 2020
  • Author: Amanda T Moon, MD; Chief Editor: William D James, MD  more...
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Laboratory Studies

Screening is conducted by determining the C4 level, which is decreased both during and in between clinical flares. If the C4 level is normal but clinical suspicion remains high, the C4 testing should be repeated, and, additionally, qualitative and functional values of C1 inhibitor (C1-INH) should be obtained. Antigenic levels of C1q are usually low and are useful to distinguish hereditary angioedema from acquired angioedema. [2]

Test results for acquired angioedema types I and II are as follows:

  • Low C1-INH level

  • Low C1q levels (except 1 reported case)

  • Low C4 and C2 levels

Acquired angioedema type II shows positive immunoblot assay findings for the 95-kd C1-INH cleavage product.

An enzyme-linked immunosorbent assay (ELISA) has been developed that measures the neutralizing capacity of anti-C1-INH antibodies in plasma. [12]

Other laboratory findings are related to associated illnesses.


Abdominal Radiography

During attacks of gastrointestinal edema, abdominal ultrasonography or computed tomography scanning may show edematous thickening of the intestinal wall, a fluid layer around the bowel, and large amounts of free peritoneal fluid.

Other findings may be referable to an associated illness.


Histologic Findings

Histologic findings are indistinguishable from other angioedema types. Features include sparse perivascular mononuclear cell infiltrate and reticular dermal, subcutaneous, or submucosal edema.

Vasodilation may be seen.