Proteinuria
Written 29th August 2020 - Last Update 23rd July 2026
Proteinuria
The upper limit of normal urinary protein excretion is 150 mg/day (24-hour collection), or a random urine protein/creatinine ratio >0.3. For albumin, normal is ~30 mg/day — 30–300 mg/day is microalbuminuria, higher is macroalbuminuria.
Mechanisms
| Mechanism | Description | Examples |
|---|---|---|
| Glomerular | Increased glomerular permeability lets plasma proteins into the filtrate | Primary: membranous nephropathy, minimal change disease, FSGS. Secondary: diabetic nephropathy, pre-eclampsia, post-infectious GN, lupus nephritis, amyloidosis |
| Tubular | Impaired proximal tubular reabsorption — mostly smaller proteins (e.g. immunoglobulin light chains), not albumin; often with other tubular defects (bicarbonate wasting, glucosuria, aminoaciduria) | Fanconi syndrome, acute tubular necrosis, tubulointerstitial nephritis, polycystic kidney disease |
| Overflow | Excess small plasma proteins (e.g. light chains in myeloma) exceed proximal tubular reabsorptive capacity | Acute monocytic leukaemia with lysozymuria, monoclonal gammopathy, multiple myeloma, myelodysplastic syndromes |
| Functional | Increased renal blood flow (exercise, fever, high-output heart failure) delivers more protein to the nephron, usually <1g/day; reverses when blood flow normalises | Fever, heart failure, intense exercise |
| Orthostatic | Benign, mostly in children/adolescents — proteinuria occurs mainly upright, so daytime urine has more protein than overnight. Excellent prognosis, no intervention needed | Unknown mechanism |
Clinical features
History: symptoms of fluid overload/hypoalbuminaemia (eye puffiness, leg/abdominal swelling, frothy urine); red/brown urine suggests GN; bone pain suggests myeloma. Ask about recent serious illness/fever, intense physical activity, known renal disease, diabetes, pregnancy, sickle cell disease, SLE, and cancer (especially myeloma).
Examination: raised BP suggests GN; peripheral oedema/ascites suggest fluid overload or low albumin.
Diagnosis
- Urine dipstick — insensitive for microalbuminuria; positive dipstick indicates overt proteinuria
- Microscopic urinalysis — casts and dysmorphic red cells suggest GN; glucose/ketones suggest diabetes
- UEC; 24-hour or random urine protein:creatinine ratio
- USS/CT KUB
- Further tests to characterise a glomerular disorder — see
nephrotic-syndrome.md - Renal biopsy if non-invasive tests are inconclusive