Hemolytic uremic syndrome is a condition that can be associated with which of the following?

• A. It can be associated with deficiencies in Factor H.
• B. It is a common cause of renal failure in adults.
• C. It never affects the kidneys.
• D. It is caused by a deficiency of C1 esterase inhibitor.

Answer: (A)

Hemolytic uremic syndrome arises when the complement system is not properly regulated, especially the alternative pathway that protects host tissues. Factor H is a key regulator that keeps this pathway in check on cell surfaces. If Factor H is deficient or dysfunctional, unchecked complement activation can occur on the endothelial cells of the kidney, leading to endothelial injury, microvascular thrombi, hemolysis, and impaired kidney function—the hallmarks of HUS. That connection makes deficiencies in Factor H a recognized association with HUS.

Deficiency of C1 esterase inhibitor, by contrast, causes hereditary angioedema rather than HUS. HUS is not a common cause of renal failure in adults, and by definition it involves the kidneys, so stating it never affects the kidneys isn’t correct.