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

Proteinuria refers to excess protein excretion in the urine — above 150 mg of total protein per day in adults, or above 30 mg/day of albumin (microalbuminuria). The normal glomerular filtration apparatus acts as a size-selective and charge-selective barrier, preventing most plasma proteins from entering the filtrate. Proteinuria indicates dysfunction of this barrier — either glomerular (the most clinically significant form), tubular, overflow, or orthostatic (postural). Microalbuminuria (30–300 mg/day of albumin, ACR 3–30 mg/mmol) is an early marker of endothelial and glomerular damage in diabetes and hypertension, preceding overt nephropathy by years. Macroalbuminuria (above 300 mg/day, ACR above 30 mg/mmol) indicates established glomerular disease. Nephrotic syndrome (above 3.5 g/day protein, or ACR above 350 mg/mmol) is defined by massive proteinuria with hypoalbuminaemia (albumin below 25 g/L), oedema (periorbital, ankle), and hyperlipidaemia. Persistent proteinuria at any level warrants systematic evaluation as it independently predicts progression to chronic kidney disease (CKD) and cardiovascular mortality — the relationship is continuous and dose-dependent.

Common glomerular causes: diabetic nephropathy (the most common cause of CKD globally — microalbuminuria progresses to macroalbuminuria then ESKD over 10–20 years without intervention), hypertensive nephrosclerosis, IgA nephropathy (the most common primary glomerulonephritis worldwide — presents with haematuria and proteinuria, often after upper respiratory infection), membranous nephropathy (commonest cause of primary nephrotic syndrome in adults; anti-PLA2R antibody-mediated), minimal change disease (most common nephrotic syndrome in children; good response to steroids), focal segmental glomerulosclerosis (FSGS — a leading cause of ESKD in young adults), lupus nephritis (common in SLE — proliferative nephritis classes III/IV are most severe), and rapidly progressive (crescentic) glomerulonephritis (ANCA-associated vasculitis — pauci-immune pattern). Systemic causes: multiple myeloma (light chain cast nephropathy — overflow proteinuria from immunoglobulin light chains), amyloidosis (AA or AL — nephrotic-range proteinuria), pre-eclampsia (new proteinuria after 20 weeks of pregnancy). Transient (benign) causes: febrile illness, strenuous exercise, and orthostatic (postural) proteinuria — protein on standing but not supine — confirm by first morning urine sample (orthostatic proteinuria: ACR normal in morning sample).

Early proteinuria is typically asymptomatic — most cases are detected on routine urine dipstick testing during health checks or monitoring of diabetes, hypertension, or other conditions. Foamy or frothy urine (persistent, non-clearing bubbles in the toilet bowl — albumin reduces surface tension) is the most notable sign visible to the patient, though it is also seen with contamination from detergent and rapid voiding. Heavy proteinuria causing nephrotic syndrome (above 3.5 g/day in adults) produces: pitting oedema (ankle and leg oedema, progressive periorbital facial puffiness — especially on waking — and in severe cases ascites and pleural effusions from low oncotic pressure); fatigue and reduced exercise tolerance from hypoalbuminaemia and anaemia; foamy urine; and features of hyperlipidaemia (xanthelasma in severe cases). In children, periorbital oedema on waking is often the presenting sign of nephrotic syndrome. Weight gain from fluid retention may be rapid (5–10 kg over days). Some patients note reduced, concentrated, or frothy urine output. IgA nephropathy may present with frank haematuria (red or brown urine — 'cola-coloured urine') synchronous with upper respiratory infections, alongside proteinuria.

Urine dipstick is the initial screen — detects albumin from trace (5–20 mg/dL) to 3+ (above 300 mg/dL); it detects albumin but not light chains (Bence-Jones protein) or tubular proteins, which require urine protein electrophoresis. Confirm persistent proteinuria with: spot first morning urine albumin-to-creatinine ratio (ACR — preferred for diabetics and CKD monitoring) or protein-to-creatinine ratio (PCR — preferred for non-diabetic glomerular disease), repeated at least twice over 3 months (orthostatic and transient causes resolve). Serum creatinine and eGFR (CKD-EPI formula) assess baseline kidney function and rate of decline. 24-hour urine protein collection: the gold standard for quantification in nephrotic syndrome and clinical trials — above 3.5 g/24h is nephrotic range. Renal ultrasound: assesses kidney size, echogenicity, obstruction (chronic small kidneys suggest long-standing CKD), and vascularity (Doppler). Further investigations guided by suspected cause: complement C3/C4 (lupus, membranoproliferative GN), ANCA (vasculitis), ANA and anti-dsDNA (lupus nephritis), anti-PLA2R antibody (membranous nephropathy — positive in 70%), serum protein electrophoresis (myeloma), blood glucose, HbA1c, and HIV. Kidney biopsy: indicated for unexplained nephrotic syndrome, rapidly progressive glomerulonephritis (eGFR falling more than 50% over 3 months), or when histological diagnosis will alter treatment — performed as day case under ultrasound guidance.

Treat the underlying cause (immunosuppression for glomerulonephritis, glycaemic control for diabetic nephropathy, antihypertensives for hypertensive nephrosclerosis). ACE inhibitors (ramipril 5–10 mg daily) or ARBs (losartan 50–100 mg, irbesartan 300 mg) are first-line antiproteinuric treatment: they reduce intraglomerular pressure by dilating the efferent arteriole, reducing protein filtration and slowing CKD progression — recommended for all patients with ACR above 3 mg/mmol (microalbuminuria) or significant proteinuria, regardless of whether BP is elevated. Target blood pressure below 130/80 mmHg (below 125/75 mmHg for significant proteinuria above 1 g/day). SGLT-2 inhibitors (dapagliflozin, empagliflozin): now first-line with ACE inhibitors in diabetic nephropathy and non-diabetic CKD with proteinuria above 200 mg/g (DAPA-CKD and CREDENCE trials — 44% risk reduction in composite renal endpoint). Mineralocorticoid receptor antagonists: finerenone reduces proteinuria and CKD progression in diabetic nephropathy. Specific treatment by cause: prednisolone for minimal change disease (90% remission in children); rituximab or tacrolimus for membranous nephropathy; rituximab or cyclophosphamide + methylprednisolone for ANCA-associated vasculitis; hydroxychloroquine, mycophenolate mofetil, and prednisolone for lupus nephritis. Statins for hyperlipidaemia in nephrotic syndrome.

Persistent proteinuria independently accelerates progression to chronic kidney disease (CKD) and end-stage renal disease (ESKD) requiring dialysis or transplantation — the rate of CKD progression correlates directly with the degree of proteinuria; reducing proteinuria below 0.5 g/day substantially slows progression. Nephrotic syndrome complications: venous thromboembolism (DVT, pulmonary embolism, renal vein thrombosis) — urinary loss of antithrombin III and protein C/S creates a hypercoagulable state; DVT prophylaxis and anticoagulation are required in severe nephrotic syndrome (albumin below 20 g/L). Severe hyperlipidaemia (cholesterol above 10 mmol/L is common in minimal change disease) — accelerates cardiovascular disease and requires statin therapy. Increased infection risk: loss of immunoglobulins and complement factors in urine causes immunodeficiency — particularly susceptibility to encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae) — vaccination and prophylactic penicillin V may be indicated in severe cases. Protein malnutrition: massive daily protein loss from the kidney causes hypoalbuminaemia, muscle wasting, impaired wound healing, and oedema. Accelerated cardiovascular disease: proteinuria is an independent cardiovascular risk factor, equivalent in magnitude to smoking or diabetes — patients with nephrotic syndrome have markedly elevated MI and stroke risk.

Control blood pressure rigorously: target below 130/80 mmHg for all patients with CKD and proteinuria; below 125/75 mmHg for those with proteinuria above 1 g per day. First-line antihypertensives are ACE inhibitors (ramipril 5-10 mg) or ARBs (losartan 50-100 mg) for their specific antiproteinuric effect beyond blood pressure reduction — they dilate the efferent arteriole, reducing intraglomerular pressure and protein filtration independently of systemic blood pressure lowering. Optimise blood glucose control (HbA1c target below 7% / 53 mmol/mol) — intensive glucose control in UKPDS and ACCORD trials reduced the onset and progression of diabetic nephropathy and proteinuria. Use SGLT-2 inhibitors (empagliflozin 10 mg or dapagliflozin 10 mg) in all patients with diabetic nephropathy or non-diabetic CKD with significant proteinuria (ACR above 200 mg/g) — DAPA-CKD trial demonstrated 44% risk reduction in composite renal endpoint and cardiovascular death, independent of glycaemic effect. Avoid nephrotoxic drugs: NSAIDs (ibuprofen, naproxen, diclofenac — reduce renal prostaglandin synthesis; harmful when eGFR is below 45); IV contrast agents (use iso-osmolar contrast with pre-hydration when eGFR is below 30); aminoglycoside antibiotics; herbal preparations containing aristolochic acid (Chinese herb nephropathy). Maintain a healthy weight (BMI below 25) and follow a low-sodium diet (below 5 g of salt per day — reduces glomerular hyperfiltration and potentiates ACE inhibitor antiproteinuric effect). Regular monitoring: urine ACR and eGFR at least annually in all people with diabetes or hypertension; every 3-6 months for established CKD or proteinuria. Nephrology referral for eGFR below 45 mL/min/1.73m² or ACR persistently above 100 mg/mmol.

See your GP for: urine that is persistently foamy or frothy (most noticeable in the toilet bowl — a sign of excess albumin in urine), ankle or facial swelling not explained by other causes, unexplained fatigue with leg oedema (possible nephrotic syndrome). Proteinuria detected incidentally on urine dipstick should be confirmed with a morning spot urine albumin-to-creatinine ratio (ACR) — a single positive dipstick does not confirm persistent proteinuria. Seek urgent assessment from GP or renal emergency unit for: nephrotic syndrome (massive ankle and facial oedema, foamy urine, breathlessness from pleural effusion — risk of venous thromboembolism and serious infection is high); rapidly rising creatinine with declining urine output (acute kidney injury — same-day assessment); blood and protein in urine simultaneously (possible rapidly progressive glomerulonephritis requiring urgent immunosuppressive treatment and early nephrology input). All patients with eGFR below 45 mL/min/1.73m² or persistent proteinuria above 100 mg/mmol ACR should be under nephrology care for specialist management and monitoring.