In nephrotic syndrome, edema is primarily caused by what mechanism?

• A. Increased capillary hydrostatic pressure
• B. Decreased plasma oncotic pressure due to hypoalbuminemia
• C. Increased plasma oncotic pressure
• D. Decreased aldosterone

Answer: (B)

Edema in nephrotic syndrome mainly results from a fall in plasma oncotic pressure due to hypoalbuminemia from heavy urinary protein loss. Albumin helps keep fluid inside blood vessels; when its level drops, fluid is more likely to move into the interstitial space, leading to edema. While the body may later retain sodium and water as a compensatory response, that secondary fluid retention is not the primary cause of the swelling. The other ideas don’t fit because increasing capillary hydrostatic pressure would require another condition (like heart failure), increasing oncotic pressure would pull fluid into vessels (reducing edema), and decreasing aldosterone would tend to lessen, not cause, edema.