A 24-year-old woman has repeated episodes of painless, nonpruritic swelling of the face, lips, and hands lasting 2 to 3 days. One episode involved laryngeal edema requiring intubation. Urticaria is never present. Her father had similar episodes. Which finding during an attack would best confirm the diagnosis?

• A Markedly elevated total IgE with positive food-specific IgE
• B High-titer antinuclear antibody
• C Positive basophil activation test to peanut extract
• D Low serum C4 level ✓

Explanation

This is hereditary angioedema due to C1 esterase inhibitor (C1-INH) deficiency. Unchecked C1r and C1s cleave C4 continuously, so serum C4 is persistently low even between attacks, making it the screening test of choice; C1q is usually normal in the hereditary form. The edema is bradykinin mediated, which explains the absence of urticaria and poor response to antihistamines and adrenaline, features that distinguish it from ordinary allergic angioedema.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.