Nephrotic syndrome
Formal Definition
A clinical syndrome defined by massive proteinuria (>3.5 g/day in adults), hypoalbuminemia (serum albumin <3 g/dL), edema (peripheral and periorbital), and hyperlipidemia (elevated LDL cholesterol); results from increased glomerular permeability to plasma proteins, most commonly due to minimal change disease, focal segmental glomerulosclerosis (FSGS), membranous nephropathy, or diabetic nephropathy; associated with hypercoagulability (loss of antithrombin III in urine) and increased infection risk.
How It's Used on the Ward
"Nephrotic" — the patient is spilling enormous amounts of protein in their urine (like a broken filter), their blood is getting dilute and protein-poor (low albumin), they are swelling up (edema from low oncotic pressure), and their cholesterol is sky high; the three classic signs are swelling, frothy urine, and low albumin.
Example
""32-year-old male presents with 2 weeks of progressive lower extremity edema and periorbital swelling. Urine: 4+ protein on dipstick, spot urine protein/creatinine ratio 6.2 (massive proteinuria), 24h urine protein 6.8 g (nephrotic range >3.5). Serum albumin 1.8 g/dL, total cholesterol 340 mg/dL, LDL 240. No hematuria, normal complement levels. Diagnosis: nephrotic syndrome. Kidney biopsy deferred — in age 30s without diabetes, minimal change disease most likely, empiric prednisone trial first; if no response in 8 weeks, proceed to biopsy."
Clinical Context
Nephrotic vs nephritic: nephrotic = heavy proteinuria, hypoalbuminemia, edema, hyperlipidemia; nephritic = hematuria, RBC casts, hypertension, mild-moderate proteinuria, low complement. Causes by age: children → minimal change disease (most common, excellent steroid response), FSGS; adults → membranous nephropathy, FSGS, diabetic nephropathy. Complications: (1) Hypercoagulable state — loss of antithrombin III in urine → venous thromboembolism (renal vein thrombosis most feared), PE, DVT. (2) Infection — loss of immunoglobulins → spontaneous bacterial peritonitis, cellulitis, meningitis. (3) Edema — from low oncotic pressure (hypoalbuminemia) + sodium retention. Treatment: treat underlying cause, sodium restriction, diuretics (loop diuretics for edema), ACE inhibitors (reduce proteinuria, protect kidney), statins (for hyperlipidemia), anticoagulation if serum albumin <2.5 + other risk factors.