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Chronic Urticaria — SCE Dermatology MCQ

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HardInflammatory DermatosesChronic UrticariaSCE Dermatology

A 40-year-old woman has chronic urticaria. Her dermatologist performs the autologous serum skin test (ASST). A wheal ≥1.5 mm larger than the negative control develops at the autologous serum injection site. What does a positive ASST suggest?

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Correct answer: D — Presence of circulating histamine-releasing autoantibodies (autoimmune urticaria)

The autologous serum skin test (ASST) is a simple in vivo screening test for autoimmune chronic spontaneous urticaria. Autologous serum is injected intradermally alongside saline (negative control) and histamine (positive control). A wheal ≥1.5 mm larger than the saline control at 30 minutes suggests the presence of circulating histamine-releasing factors (IgG autoantibodies against FcεRI or anti-IgE). A positive ASST indicates type IIb autoimmune CSU. While not highly specific (false positives occur), it identifies patients more likely to respond to immunomodulatory therapy and less likely to respond to Omalizumab alone. The basophil histamine release assay is the gold-standard confirmatory test but is not widely available.

Reference: EAACI/GA²LEN 2022 Urticaria; BAD