A 5-year-old boy with nephrotic syndrome is found to have heavy proteinuria, hypoalbuminemia, and generalized edema. The current understanding of the primary mechanism responsible for edema formation in nephrotic syndrome is:

• A Decreased antidiuretic hormone secretion
• B Secondary hyperaldosteronism due to underfilled circulation
• C Increased capillary hydrostatic pressure
• D Primary renal sodium retention due to intrarenal mechanism ✓

Explanation

In minimal change disease and most childhood nephrotic syndrome, edema results from primary renal sodium retention due to an intrarenal defect in sodium handling, not simply from hypoalbuminemia. The underfill hypothesis (secondary hyperaldoseronism from reduced effective circulatory volume) applies to some cases but the overfill/primary sodium retention mechanism is now considered primary in most nephrotic patients, particularly children.

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

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