Which laboratory finding best characterizes hereditary angioedema?

Which laboratory finding best characterizes hereditary angioedema?

• A. Decreased activity of C1 inhibitor
• B. Decreased activity of C3
• C. Increased activity of C1 inhibitor
• D. Increased activity of C2

Answer: (A)

Hereditary angioedema is due to deficiency or dysfunction of C1 esterase inhibitor (C1-INH). C1-INH normally keeps the classical complement pathway and the kallikrein-kinin system in check, preventing excessive bradykinin production. When C1-INH is low or defective, C1 activation proceeds unchecked, leading to increased bradykinin and angioedema. The key laboratory finding that best characterizes this condition is decreased activity of C1-INH. C4 levels are often low due to consumption, but C1-INH deficiency is the defining feature. Other components like C3 or C2 aren’t specifically reduced in hereditary angioedema, and increased C1-INH activity would not explain the syndrome.

Hereditary angioedema is due to deficiency or dysfunction of C1 esterase inhibitor (C1-INH). C1-INH normally keeps the classical complement pathway and the kallikrein-kinin system in check, preventing excessive bradykinin production. When C1-INH is low or defective, C1 activation proceeds unchecked, leading to increased bradykinin and angioedema. The key laboratory finding that best characterizes this condition is decreased activity of C1-INH. C4 levels are often low due to consumption, but C1-INH deficiency is the defining feature. Other components like C3 or C2 aren’t specifically reduced in hereditary angioedema, and increased C1-INH activity would not explain the syndrome.