Heavy proteinuria (>3.5 g/day) with hypoalbuminemia, edema, and hyperlipidemia.
Also known as: nephrotic syndrome, minimal change disease, FSGS, membranous nephropathy, diabetic nephropathy
Overview
A glomerular disorder characterized by proteinuria >3.5 g/day (or UPCR >3.5 g/g), hypoalbuminemia (<3.0 g/dL), peripheral edema, and hyperlipidemia. Reflects increased glomerular basement membrane permeability to plasma proteins.
Epidemiology
Annual incidence ~3 per 100,000 adults. Minimal change disease is the most common cause in children; FSGS and membranous nephropathy dominate in adults. Diabetic nephropathy is the most common secondary cause overall.
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Question 1RenalEasy
A 35-year-old male presents with generalized edema. A 24-hour urine collection contains 4 g of protein, serum albumin is 2.2 g/dL, and LDL cholesterol is 230 mg/dL. Renal biopsy electron microscopy shows diffuse podocyte foot process effacement. Which of the following is the most likely diagnosis?
ANephritic syndrome
BPostural proteinuria
CTubular proteinuria
DNephrotic syndrome
EOverflow proteinuria
Reveal answer & full explanation
Correct answer: D — Nephrotic syndrome
ANephritic syndrome
BPostural proteinuria
CTubular proteinuria
DNephrotic syndrome✓
EOverflow proteinuria
Why Nephrotic syndrome is correct
The presentation meets the classic criteria for nephrotic syndrome: >3.5 g/day proteinuria (4 g here), hypoalbuminemia (<3.0 g/dL; 2.2 g/dL here), generalized edema, and hyperlipidemia (LDL 230 mg/dL here).
Diffuse podocyte foot process effacement on electron microscopy (EM) is the hallmark finding of nephrotic-range glomerular disease (minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS)).
Why the others are wrong
Nephritic syndrome — presents with hematuria, red blood cell (RBC) casts, mild proteinuria, hypertension, and acute kidney injury (AKI); different pathology (post-streptococcal GN, IgA nephropathy, lupus, ANCA vasculitis) and does not show diffuse foot process effacement.
Postural proteinuria — also called orthostatic proteinuria; a benign condition of adolescents and young adults in which protein appears only in upright urine (the first-morning sample is normal), usually under 1 g/day; it does not cause edema, hypoalbuminemia, or hyperlipidemia, and kidney histology is normal.
Tubular proteinuria — results from impaired proximal tubular reabsorption of filtered low-molecular-weight proteins (such as beta-2 microglobulin) in tubulointerstitial disease; it is usually under 2 g/day, does not cause hypoalbuminemia, edema, or hyperlipidemia, and the injury is tubular rather than podocyte foot process effacement.
Overflow proteinuria — occurs when filtered low-molecular-weight proteins, classically monoclonal light chains in multiple myeloma, exceed the tubules' reabsorptive capacity, and a 24-hour collection can show gram amounts of protein; but the glomerular barrier is intact, so albumin loss is minimal and it does not cause hypoalbuminemia, edema, hyperlipidemia, or diffuse podocyte foot process effacement.
Complications: venous thromboembolism (VTE) risk (loss of antithrombin III), infection susceptibility (loss of immunoglobulins), AKI.
Treatment depends on the underlying cause; many primary glomerular diseases are treated with steroids.
Question 2RenalMedium
A 9-year-old boy has periorbital edema, ascites, and frothy urine. Urinalysis shows 4+ protein and oval fat bodies, and serum albumin is 1.4 g/dL. Two days later, he develops abrupt left flank pain and gross hematuria. He has left flank tenderness. Ultrasound shows an enlarged left kidney, 2 cm longer than the right, with loss of corticomedullary differentiation. Which of the following is the most likely cause of these new findings?
AObstructing ureteral stone
BAcute bacterial pyelonephritis
CCrescentic glomerulonephritis
DAcute renal vein thrombosis
ESegmental kidney infarction
Reveal answer & full explanation
Correct answer: D — Acute renal vein thrombosis
AObstructing ureteral stone
BAcute bacterial pyelonephritis
CCrescentic glomerulonephritis
DAcute renal vein thrombosis✓
ESegmental kidney infarction
Why Acute renal vein thrombosis is correct
Step 1: edema, ascites, 4+ proteinuria, oval fat bodies, and a serum albumin of 1.4 g/dL establish nephrotic syndrome (at age 9, most often minimal change disease).
Step 2: nephrotic syndrome is hypercoagulable. Urinary loss of antithrombin and plasminogen, together with increased hepatic synthesis of fibrinogen and factors V and VIII and hemoconcentration, tips the balance toward venous thrombosis, and the risk climbs as serum albumin falls.
Abrupt flank pain, gross hematuria, and one enlarged kidney that has lost corticomedullary differentiation is the classic picture of renal vein thrombosis: blocked venous outflow congests and swells the kidney. Worsening proteinuria and a fall in GFR may accompany it.
Doppler ultrasound, CT venography, or MR venography confirms the clot; treatment is anticoagulation.
Why the others are wrong
Crescentic glomerulonephritis - It can cause gross hematuria, but it is a bilateral nephritic process (red cell casts, hypertension, azotemia over days to weeks) that does not produce abrupt one-sided flank pain with a single swollen kidney, and minimal change disease does not typically evolve into crescentic disease (the trap is equating gross hematuria with glomerulonephritis).
Obstructing ureteral stone - Renal colic is colicky pain that radiates toward the groin, and its ultrasound hallmark is hydronephrosis, often with a shadowing calculus, rather than swollen parenchyma that has lost corticomedullary differentiation; stones are also far less common in children than in adults (the trap is the flank pain plus hematuria reflex).
Segmental kidney infarction - Infarction from renal arterial thrombosis or embolism does occur in nephrotic syndrome, but far less often than venous thrombosis. Hematuria, when present, is more often microscopic than gross, and the ultrasound is often unremarkable: contrast CT shows a wedge-shaped perfusion defect in a kidney of normal size rather than diffuse congestive enlargement with loss of corticomedullary differentiation (the trap is treating arterial and venous occlusion as interchangeable).
Acute bacterial pyelonephritis - Children with nephrotic syndrome are infection-prone, and pyelonephritis can enlarge the kidney and blur corticomedullary differentiation on ultrasound. But no fever or dysuria is described, pyelonephritis usually builds over hours to days rather than striking abruptly, and gross hematuria is uncommon with it; abrupt flank pain with gross hematuria when the albumin is 1.4 g/dL points to venous thrombosis (the trap is blaming infection for every new nephrotic complication).
Additional high-yield points
In children with nephrotic syndrome, infection (spontaneous peritonitis, classically from Streptococcus pneumoniae, and cellulitis) and AKI from intravascular volume depletion are more common complications than thrombosis; fever with abdominal pain and ascites should prompt evaluation for peritonitis. Thrombosis becomes the leading concern when the presentation looks like this one.
Thromboembolic risk is highest in adults with membranous nephropathy. In children it is higher with age over 12, severe hypoalbuminemia, congenital nephrotic syndrome, and central venous catheters.
Other sites include the deep veins of the legs, the pulmonary arteries (embolism), and the cerebral venous sinuses, a site worth remembering in children.
Low antithrombin levels can blunt the anticoagulant response to heparin.
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Damage to the glomerular filtration barrier (podocytes, GBM, endothelium) increases permeability to albumin and larger proteins. Proteinuria drives hypoalbuminemia → reduced oncotic pressure → edema. Hepatic compensatory synthesis raises lipoproteins (hyperlipidemia). Loss of antithrombin III, protein C/S, and immunoglobulins predisposes to thrombosis and infection.
Clinical presentation
Symptoms
Insidious or rapid-onset peripheral edema — periorbital in morning, dependent later
Foamy or frothy urine (proteinuria)
Weight gain, abdominal distention (ascites)
Dyspnea (pleural effusions), fatigue
Symptoms of underlying cause: rash, joint pain (SLE), polyuria/polydipsia (diabetes)
Muehrcke lines (transverse white nail bands), xanthelasma
Classic findings
Periorbital edema in a child = consider minimal change disease until proven otherwise.
Differential diagnosis
Minimal change disease — Most common in children; abrupt nephrotic onset; normal light microscopy; podocyte effacement on EM; steroid-responsive
Focal segmental glomerulosclerosis (FSGS) — Common in adults, especially Black patients (APOL1); HIV, obesity, heroin; segmental sclerosis on biopsy
Membranous nephropathy — Most common primary nephrotic syndrome in white adults; anti-PLA2R antibody positive in ~70% primary; subepithelial deposits, 'spike and dome'
Nephrotic syndrome diagnosed by: nephrotic-range proteinuria (>3.5 g/day in adults; UPCR ≥2 g/g or 3+ dipstick in children) plus hypoalbuminemia <3.0 g/dL, usually with edema; hyperlipidemia and lipiduria are typical but not required. Kidney biopsy is standard in adults to determine specific pathology and guide therapy (excepting clear diabetic nephropathy).
Labs
24-h urine protein OR spot UPCR (>3.5 g/g diagnostic)
Urinalysis with microscopy — oval fat bodies, fatty casts, 'Maltese cross' under polarized light
Serum albumin (<3.0 g/dL), lipid panel (elevated), creatinine, BMP
Hep B, Hep C, HIV serologies
ANA, complement (C3, C4), SPEP/UPEP with free light chains
Loop diuretic — furosemide, torsemide, bumetanide — for edema; may need higher doses due to albumin binding loss
Statin (atorvastatin, rosuvastatin) for hyperlipidemia
Sodium restriction (<2 g/day)
Second-line / adjunct
Minimal change disease: prednisone (children 60 mg/m²/day or 2 mg/kg/day for 4-6 weeks, then alternate-day for another 4-6 weeks; adults 1 mg/kg/day until remission, up to 16 weeks); cyclophosphamide or rituximab for relapses
FSGS: prednisone trial; cyclosporine, tacrolimus, or rituximab for steroid-resistant/dependent
Membranous nephropathy: supportive care alone if low risk (spontaneous remission common); if at risk of progression, rituximab first-line (KDIGO 2021); alternative cyclophosphamide + steroid (Ponticelli) or calcineurin inhibitor
Full anticoagulation for any VTE; consider prophylactic anticoagulation (warfarin, often started with LMWH) in membranous with albumin <2.5 g/dL (highest VTE risk) when bleeding risk is acceptable
Pneumococcal vaccination; consider prophylactic antibiotics if recurrent infections
Complications
Venous thromboembolism — especially renal vein thrombosis in membranous nephropathy (highest risk)
Increased infection risk (loss of immunoglobulins, complement; immunosuppression)
Acute kidney injury from volume depletion (over-diuresis) or thrombosis
Progression to CKD/ESRD
Accelerated atherosclerosis from chronic dyslipidemia
Vitamin D deficiency (urinary loss of vitamin D binding protein)
Membranous nephropathy has the highest VTE risk of any nephrotic disease — especially renal vein thrombosis (flank pain, hematuria, AKI).
Anti-PLA2R antibody is diagnostic for primary membranous; positive in ~70%. Evaluate every membranous patient for secondary causes (malignancy, hepatitis B, SLE, drugs) regardless of anti-PLA2R status.
Children with new-onset nephrotic syndrome (age 1-10) are presumed minimal change — empiric steroids without biopsy unless atypical features.
Avoid over-diuresis: rapid volume loss with low albumin can precipitate AKI and worsen edema rebound.
References
KDIGO 2021 — KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases (Kidney Int 2021)
Beck 2009 — M-type Phospholipase A2 Receptor as Target Antigen in Idiopathic Membranous Nephropathy (Beck et al., NEJM 2009)
KDIGO 2025 — KDIGO 2025 Clinical Practice Guideline for the Management of Nephrotic Syndrome in Children (Kidney Int 2025;107(5S):S241-S289)
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