A 22-year-old man has recurrent episodes of painful lip and hand swelling since adolescence, sometimes with abdominal colic. His father has similar episodes. During an attack, which laboratory finding is expected?

• A Low C4 level ✓
• B Normal C4 with reduced C1q
• C Raised total IgE with positive thyroid autoantibodies
• D Positive basophil activation test to food allergen

Explanation

Hereditary angioedema due to C1 esterase inhibitor deficiency (type I) or dysfunctional inhibitor (type II) is autosomal dominant and bradykinin mediated. C4 is characteristically low both during and between attacks and serves as the screening test, followed by C1-INH antigenic and functional assays. Attacks do not respond well to antihistamines or adrenaline because histamine is not the mediator. Low C1q points toward acquired C1-INH deficiency instead.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.