A 12-year-old boy is brought to the emergency department by his mother because of progressive shortness of breath, difficulty speaking, and diffuse, colicky abdominal pain for the past 3 hours. Yesterday he underwent a tooth extraction. His father and a paternal uncle have a history of repeated hospitalizations for upper airway and orofacial swelling. The patient takes no medications. His blood pressure is 112/62 mm Hg. Examination shows edematous swelling of the lips, tongue, arms, and legs; there is no rash. Which of the following studies is most likely to be abnormal?

Question

Quizplus · Accepted Answer

Eductional Objective: Hereditary angioedema is characterized by recurrent episodes of cutaneous and/or mucosal swelling due to C1 inhibitor deficiency.  C4 levels are low due to uninhibited cleavage of C4 by excess activated C1.

A 12-Year-Old Boy Is Brought to the Emergency Department by His