Protein in Urine (Proteinuria) — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Proteinuria (protein in the urine) is the abnormal excretion of protein in the urine, normally below 150 mg per day. The glomerular filtration barrier normally prevents most plasma proteins from entering the urine. When this barrier is damaged, albumin and other proteins leak into the filtrate. Proteinuria is detected on urine dipstick testing (semi-quantitative) and quantified by the albumin:creatinine ratio (ACR) or protein:creatinine ratio (PCR) on a spot urine sample, or 24-hour urine collection. It affects approximately 10% of adults globally and is a cardinal sign of kidney disease. Persistent proteinuria ≥30 mg/g (ACR ≥3 mg/mmol) defines chronic kidney disease and is independently associated with progression to end-stage renal disease, cardiovascular events, and premature mortality. Nephrotic syndrome is defined by massive proteinuria (>3.5 g/day), hypoalbuminaemia (<25 g/L), oedema, and hyperlipidaemia.

Glomerular proteinuria (most common): diabetic nephropathy — the most common cause of proteinuria in adults globally (microalbuminuria evolves to macroalbuminuria as diabetic kidney disease progresses); hypertensive nephropathy; glomerulonephritis (IgA nephropathy — most common primary GN worldwide; membranous nephropathy — most common cause of nephrotic syndrome in non-diabetic adults >40; focal segmental glomerulosclerosis — FSGS; minimal change disease — most common in children; lupus nephritis). Tubular proteinuria: Fanconi syndrome, tubulointerstitial nephritis, toxin exposure (NSAIDs, cisplatin). Overflow proteinuria: multiple myeloma (light chain proteinuria — Bence Jones protein — detected by urine protein electrophoresis, not standard dipstick). Functional/transient proteinuria (benign): heavy exercise, orthostatic proteinuria (young adults — protein appears in upright position only), fever, heart failure. Risk factors for progressive proteinuria: diabetes (poor glycaemic control), hypertension, obesity, NSAIDs, contrast nephropathy, and nephrotoxic antibiotics.

Mild-moderate proteinuria is usually asymptomatic — discovered incidentally on urine testing. Foamy or frothy urine is the characteristic symptom of heavy proteinuria (nephrotic range ≥3.5 g/day) — caused by surface-active protein molecules. Nephrotic syndrome causes: pitting oedema (periorbital — especially prominent in the morning; ankle and leg oedema worsening throughout the day; abdominal ascites; scrotal or labial oedema in severe cases); weight gain from fluid retention; fatigue; hypertension; and in heavy protein loss, frothy urine. Nephrotic syndrome complications: increased infection risk (immunoglobulin loss — peritonitis, pneumococcal infections), thromboembolism (loss of antithrombin III and protein C/S — renal vein thrombosis, DVT, pulmonary embolism risk is high), and dyslipidaemia (atherosclerotic risk). Nephritic syndrome (glomerulonephritis): haematuria, hypertension, oliguria, and mild proteinuria — may progress to rapidly progressive GN requiring emergency treatment.

Urine dipstick: detects albumin semi-quantitatively (trace = 150–300 mg/L; 1+ = 300–1,000 mg/L; 2+ = 1,000–3,000 mg/L; 3+ = >3,000 mg/L). Insensitive to light chains (myeloma). Spot urine albumin:creatinine ratio (ACR): corrects for urine concentration — preferred test. ACR <3 mg/mmol = normal; 3–30 mg/mmol = moderately increased (microalbuminuria); >30 mg/mmol = severely increased (macroalbuminuria/proteinuria). Protein:creatinine ratio (PCR): >45 mg/mmol corresponds to >300 mg/day (nephrotic range >300 mg/mmol). 24-hour urine collection for protein excretion: gold standard for quantification; nephrotic syndrome = >3.5 g/day (>3,500 mg/day). Urine microscopy: red cell casts and dysmorphic red cells indicate glomerulonephritis. Blood tests: eGFR, serum albumin (low in nephrotic), complement C3/C4 (low in lupus nephritis, MPGN), ANCA (vasculitis), anti-GBM (Goodpasture's), ANA/anti-dsDNA (SLE), serum protein electrophoresis (myeloma). Renal biopsy: gold standard for diagnosis of primary glomerular disease — determines histological type guiding specific immunosuppressive treatment.

Treat the underlying cause: optimal glycaemic control (HbA1c <53 mmol/mol in diabetic nephropathy), aggressive blood pressure control (target <130/80 mmHg), immunosuppression for primary glomerulonephritis. ACE inhibitors (ramipril, lisinopril) or ARBs (losartan, irbesartan) are first-line antiproteinuric therapy — reduce proteinuria by 40–50% and slow CKD progression independently of blood pressure effect; should be titrated to maximum tolerated dose. Do not combine ACE inhibitor + ARB (dual RAS blockade increases adverse events without additional benefit). SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin): now standard of care for diabetic nephropathy and non-diabetic proteinuric CKD — reduce proteinuria by 20–30% and reduce risk of CKD progression by 35–40% (CREDENCE, DAPA-CKD, EMPA-KIDNEY trials). Finerenone (non-steroidal mineralocorticoid receptor antagonist): reduces proteinuria and CKD progression in type 2 diabetes with CKD. Minimal change disease: prednisolone (1 mg/kg/day) induces complete remission in 90% of children and 75–80% of adults within 8 weeks. Membranous nephropathy: rituximab (anti-CD20) is now preferred first-line for high-risk patients (replacing cyclophosphamide). FSGS: steroids ± calcineurin inhibitors. Lupus nephritis: hydroxychloroquine + mycophenolate mofetil + prednisolone (class III/IV) ± voclosporin or belimumab. Oedema: loop diuretics (furosemide); salt restriction.

Persistent proteinuria is both a marker and driver of progressive chronic kidney disease (CKD). Each 1 g/day increase in proteinuria is independently associated with faster glomerular filtration rate (GFR) decline — tubular toxicity from filtered proteins and glomerular hypertension from protein-induced inflammation accelerate nephron loss. Without treatment, overt diabetic nephropathy (proteinuria above 300 mg/day) progresses to end-stage renal disease (ESRD) in 15-25% of patients over 15 years; proteinuria reduction with ACE inhibitors or ARBs reduces this progression rate by 50%. In IgA nephropathy, proteinuria above 1 g/day at presentation predicts 20-30% risk of ESRD over 20 years. Nephrotic-range proteinuria (above 3.5 g/day) causes the full nephrotic syndrome with its attendant complications (hypoalbuminaemia, oedema, hypercoagulability, dyslipidaemia, and infection risk). Massive proteinuria causes severe malnutrition and growth retardation in children. Cardiovascular disease risk is markedly elevated with proteinuria — even microalbuminuria (30-300 mg/day) is an independent risk factor for cardiovascular events in patients with and without diabetes. Hypertension, a consequence of glomerular disease causing sodium retention and renin-angiotensin system activation, amplifies the rate of renal progression and increases cardiovascular risk further. End-stage renal disease requiring dialysis or kidney transplantation represents the terminal complication of untreated progressive proteinuric nephropathy.

Control diabetes meticulously — HbA1c below 53 mmol/mol (7%) prevents and slows diabetic nephropathy. Treat hypertension aggressively — blood pressure below 130/80 mmHg with an ACE inhibitor or ARB protects the kidneys. Start SGLT2 inhibitors early in patients with type 2 diabetes and any degree of albuminuria (ACR ≥3 mg/mmol) regardless of eGFR. Avoid nephrotoxins: NSAIDs (worsen proteinuria and accelerate CKD), IV contrast (use with caution in CKD; pre-hydrate; use iso-osmolar contrast), aminoglycoside antibiotics. Maintain healthy body weight — obesity causes glomerulomegaly and proteinuria. Limit dietary protein to 0.8–1.0 g/kg/day in CKD (high protein intake increases intraglomerular pressure). Low-sodium diet (<2 g/day) reduces oedema and blood pressure. Annual urine ACR testing in all patients with diabetes or hypertension — early detection enables timely intervention.

See a doctor promptly if you notice persistent foamy or frothy urine, swelling of the legs, face, or abdomen, or if a routine urine test shows protein on dipstick. Seek emergency care for sudden, severe facial or leg swelling with breathlessness (acute nephrotic syndrome), blood in the urine with reduced urine output and high blood pressure (nephritic syndrome — may indicate rapidly progressive glomerulonephritis requiring urgent biopsy and immunosuppression), or acute deterioration in kidney function. All patients with diabetes should have annual ACR testing from diagnosis (type 2 diabetes) or 5 years after diagnosis (type 1 diabetes) — microalbuminuria is the earliest detectable sign of diabetic nephropathy and is fully reversible if treated early.