Synopsis
Detect and quantify urinary protein accurately, distinguish albumin, tubular and overflow mechanisms, recognise nephrotic or nephritic urgency and use albuminuria to guide CKD risk and treatment.
- Use urine albumin-to-creatinine ratio as the first-line quantitative test in non-pregnant adults because it detects lower-level albumin leakage better than dipstick or PCR.
- NICE classifies A1 as ACR below 3 mg/mmol, A2 as 3 to 30 mg/mmol and A3 as above 30 mg/mmol; albuminuria changes risk even when eGFR is preserved.
- Confirm an ACR from 3 to 70 mg/mmol on a subsequent early-morning sample in a stable adult. NICE does not require confirmation before action when the initial ACR is at least 70 mg/mmol.
- Fever, strenuous exercise, UTI, decompensated heart failure, hyperglycaemia, menstruation and marked hypertension can cause transient albuminuria; resolve context without ignoring a very high result.
- Glomerular protein is predominantly albumin. Tubular disease loses low-molecular-weight proteins, while overflow protein such as immunoglobulin light chains may produce a high PCR with relatively modest ACR.
- A negative or weak dipstick does not exclude light-chain proteinuria. Suspected myeloma requires serum free light chains, immunoglobulins and protein electrophoresis/immunofixation under the local pathway.
- Nephrotic syndrome combines heavy protein loss with hypoalbuminaemia and oedema, often hyperlipidaemia, and increases venous thrombosis and infection risk. The cause still requires biopsy-led nephrology assessment.
- Blood plus protein, hypertension and impaired renal function is nephritic until assessed; this pattern is more urgent than isolated stable albuminuria in diabetes.
- ACE inhibitors or ARBs and SGLT2 inhibitors reduce albuminuria and kidney risk in defined NICE populations, but require potassium, creatinine, volume and pregnancy review.
- Monitor proportional and absolute ACR change with the same collection conditions. Small fluctuations are biological noise; disappearance of protein during severe filtration loss is not necessarily recovery.
Key red flags
Generalised oedema, very heavy proteinuria, low serum albumin and often high lipids suggests nephrotic syndrome. Unilateral leg swelling, pleuritic pain, fever or abdominal pain may indicate thrombosis or infection.
Albuminuria with haematuria, red-cell casts, hypertension, oliguria and rising creatinine supports inflammatory glomerular disease. Pulmonary or systemic features make it a renal emergency.
Bone pain, anaemia, hypercalcaemia, recurrent infection or AKI with discordantly high PCR and low ACR suggests a non-albumin protein such as monoclonal free light chain.
Investigation priorities
Confirm and classify albumin leakage while reducing postural and concentration variation.
Management branches
Positive dipstick protein or ACR at least 3 mg/mmol without current severe illness.
- Check UTI, menstruation, exercise, fever, glucose and heart failure, then confirm ACR 3 to 70 using an early-morning sample; do not delay action for ACR at least 70.
- Assign A category with eGFR G category, check blood pressure and diabetes, review medicines and calculate progression or KFRE where NICE applies.
- Start indicated kidney-protective treatment and monitoring, referring for high ACR, haematuria, rapid decline, resistant hypertension, young age or uncertain cause.