A 56-year-old male presents with edema, hypoalbuminemia, heavy proteinuria, and lipiduria with a normal GFR. What is the most likely diagnosis?

• A. Pyelonephritis
• B. Congestive heart failure
• C. Nephrotic syndrome
• D. Prostatitis

Answer: (C)

Nephrotic syndrome is defined by heavy proteinuria (more than 3.5 g/day), hypoalbuminemia, edema, and often lipid abnormalities with lipiduria. Here, edema and low albumin come from urinary loss of albumin, which reduces plasma oncotic pressure and promotes fluid leakage into interstitial spaces. The very large amount of protein lost in the urine fits nephrotic-range proteinuria, and lipiduria occurs as the liver increases lipoprotein production to compensate for hypoalbuminemia, with lipids spilling into the urine. GFR can be normal in nephrotic syndrome, especially early on or with some etiologies, so preserved filtration rate doesn’t exclude it. This constellation isn’t typical for pyelonephritis (infection signs without major protein loss and lipiduria), congestive heart failure (edema can occur but heavy proteinuria with lipiduria is not characteristic), or prostatitis (renal protein loss and lipiduria are not features).