Proteinuria and albuminuria

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Healthy glomeruli restrict large proteins and proximal tubules reclaim filtered low-molecular-weight proteins. Glomerular barrier injury therefore produces albuminuria; tubular injury produces smaller proteins; plasma overproduction can overwhelm normal reabsorption. ACR answers the common glomerular-risk question but cannot describe every mechanism.

Albuminuria is both diagnostic and prognostic. Persistent A2 or A3 can establish CKD with eGFR above 60 and independently predicts cardiovascular events and progression. NICE therefore uses the combined G and A category for monitoring, blood-pressure treatment and referral rather than reserving kidney labels for low filtration.

The urgency spectrum ranges from low stable A2 in metabolic disease to explosive nephritic-nephrotic illness. Clinical context, sediment, serum albumin, oedema, function and time course determine whether the next step is repeat confirmation, kidney-protective therapy, serology or same-day nephrology review.

Key points

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.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Glomerular protein leakage

Diabetes, immune glomerulopathies, podocyte disease and vascular injury increase filtration-barrier permeability, producing predominantly albumin-rich urine on testing.

Tubular protein loss

Proximal tubular injury prevents reabsorption of normally filtered low-molecular-weight proteins, often with other solute-wasting features and relatively modest albuminuria.

Overflow proteinuria

Excess circulating light chains or other small proteins exceed proximal reabsorptive capacity, creating a high total protein result that dipstick albumin may miss.

Transient functional albuminuria

Fever, strenuous exercise, urinary infection, severe hyperglycaemia, decompensated heart failure, menstruation and marked hypertension can temporarily increase urinary albumin.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Barrier selectivity failure
Podocyte, basement-membrane or endothelial injury allows albumin and sometimes larger plasma proteins to cross the glomerular filtration barrier.
2
Tubular reclamation failure
Injured proximal cells cannot endocytose small filtered proteins, so low-molecular-weight proteins appear in urine despite a relatively intact glomerulus.
3
Filtered-load overflow
Very high plasma concentrations of freely filtered proteins saturate normal tubular uptake and spill into urine.
4
Protein-mediated progression
Persistent filtered protein activates tubular inflammatory and fibrotic signalling, while albuminuria also marks increased cardiovascular and renal risk.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Moderately increased albuminuria

Persistent ACR 3 to 30 mg/mmol is A2 and may be the earliest diabetic, hypertensive or glomerular kidney marker. It carries cardiovascular and renal significance despite normal eGFR.

Severely increased albuminuria

ACR above 30 mg/mmol is A3. Values at least 70 mg/mmol have stronger referral and blood-pressure implications in NICE/UKKA guidance, especially without diabetes or with haematuria.

Nephrotic syndromeRed flag

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.

Nephritic proteinuriaRed flag

Albuminuria with haematuria, red-cell casts, hypertension, oliguria and rising creatinine supports inflammatory glomerular disease. Pulmonary or systemic features make it a renal emergency.

Overflow proteinRed flag

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.

Orthostatic or transient loss

Protein present later in the day but absent in an early-morning specimen can occur in benign orthostatic proteinuria in younger people; fever, exercise and acute illness produce other transient patterns.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Early-morning urine ACRFirst step
Why
Confirm and classify albumin leakage while reducing postural and concentration variation.
Interpretation and limitations
Repeat initial ACR 3 to 70 mg/mmol under stable conditions. ACR at least 70 can prompt action without a confirmatory wait, although cause and acute context still need assessment.
02
Urine PCR
Why
Quantify larger protein losses and detect non-albumin protein when used alongside ACR.
Interpretation and limitations
PCR is acceptable for monitoring high-level protein and can expose ACR/PCR discordance. UKKA notes PCR 100 mg/mmol approximates about 1 g/day only as a broad conversion.
03
Urinalysis and sediment
Why
Identify haematuria, infection and casts that change urgency and mechanism.
Interpretation and limitations
Red-cell casts or dysmorphic cells with protein favour glomerulonephritis. Pyuria may reflect infection or interstitial disease, and acute UTI can temporarily increase ACR.
04
Serum albumin, lipids, creatinine and electrolytes
Why
Assess nephrotic physiology, kidney function and treatment risk.
Interpretation and limitations
Low albumin with oedema and heavy urine loss supports nephrotic syndrome, but liver disease, inflammation and malnutrition also lower albumin. Potassium constrains RAAS blockade.
05
HbA1c, blood pressure and cardiovascular assessment
Why
Identify common drivers and quantify modifiable progression risk.
Interpretation and limitations
Diabetes and hypertension are common but should not automatically explain abrupt heavy protein, active sediment or rapid decline; atypical features require nephrology review.
06
Immunology and monoclonal protein studies
Why
Investigate immune-complex, vasculitic or paraprotein-related kidney disease in an appropriate phenotype.
Interpretation and limitations
Select ANA, complements, ANCA, anti-GBM, hepatitis/HIV, immunoglobulins, electrophoresis and free light chains with nephrology. CKD alters free-light-chain concentrations and ratio interpretation.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Transient albuminuria

A result during fever, exercise, menstruation or infection may fall when repeated on a stable early-morning sample, unlike persistent kidney damage.

Orthostatic proteinuria

Protein present during daytime activity but absent in an early-morning specimen suggests a benign postural pattern, chiefly in younger people.

False or concentration-dependent dipstick result

Highly concentrated or alkaline urine can exaggerate dipstick protein, while dilute urine can mask it; quantitative ACR or PCR clarifies the burden.

Monoclonal light-chain proteinuria

A high PCR with disproportionately low ACR, anaemia or bone symptoms suggests overflow protein and requires specific monoclonal testing.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Incidental albuminuriaConfirm and classify riskFirst stepPositive dipstick protein or ACR at least 3 mg/mmol without current severe illness.

1Check 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.
2Assign A category with eGFR G category, check blood pressure and diabetes, review medicines and calculate progression or KFRE where NICE applies.
3Start indicated kidney-protective treatment and monitoring, referring for high ACR, haematuria, rapid decline, resistant hypertension, young age or uncertain cause.

02Nephrotic presentationFind complications and cause quicklyGeneralised oedema with heavy proteinuria and low serum albumin.

1Assess respiratory status, intravascular volume, infection and venous thromboembolism; check renal function, albumin, lipids, urine sediment and a targeted secondary-cause history.
2Discuss urgently with nephrology for serology, paraprotein studies and biopsy planning; avoid assuming diabetic nephropathy when onset or sediment is atypical.
3Manage salt, oedema, thrombosis risk and blood pressure through an individual renal plan, because aggressive diuresis or anticoagulation can harm selected patients.

03Discordant ACR and PCRSearch for non-albumin proteinSubstantial total protein with little albumin, unexplained AKI or myeloma features.

1Repeat a clean sample and compare quantitative ACR with PCR rather than trusting dipstick intensity.
2Request FBC, calcium, renal profile, immunoglobulins, serum free light chains and electrophoresis/immunofixation according to the local haematology-nephrology pathway.
3EscalationEscalate suspected cast nephropathy or other monoclonal gammopathy of renal significance promptly; avoiding delay is more important than awaiting every outpatient result.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Reduces intraglomerular pressure, albuminuria, cardiovascular risk and progression in defined diabetic and non-diabetic CKD groups.

ACE inhibitor or angiotensin receptor blocker

Titrate to the highest licensed dose tolerated when NICE indications are met, using blood pressure, potassium, creatinine and volume-status monitoring.

Avoid combination ACE inhibitor plus ARB. Review pregnancy, potassium above 5, bilateral renovascular disease and AKI risk; check renal profile before and after initiation or dose increase.

Slows CKD progression and reduces cardiorenal events in eligible albuminuric and broader CKD populations.

SGLT2 inhibitor

Select the licensed agent and dose using current NICE indication, eGFR range, diabetes status and SmPC, alongside standard kidney-protective care.

Provide genital infection, volume, ketoacidosis and peri-procedure sick-day advice. Glycosuria is expected; temporarily review during severe acute illness and never use eGFR outside the licence.

Relieves clinically important oedema and pulmonary congestion while the proteinuric cause is treated.

Loop diuretic for nephrotic oedema

Nephrology-directed dose and route titrated to weight, symptoms, urine response, renal function and intravascular assessment; combination therapy may be specialist-only.

Diuretic resistance is common, but rapid escalation can cause hypovolaemia, AKI, hypokalaemia or hyponatraemia. Daily weights and biochemical monitoring are essential.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Nephrotic syndrome

Heavy glomerular loss can cause hypoalbuminaemia, generalised oedema and hyperlipidaemia, while nephrotic syndrome also increases venous thrombosis and infection risk.

Progressive kidney scarring

Sustained protein traffic damages tubules and interstitium, accelerating nephron loss alongside the underlying glomerular or systemic disease.

Cardiovascular events

Persistent albuminuria signals endothelial and vascular risk even when eGFR is preserved, identifying greater susceptibility to heart failure and atherosclerotic events.

Acute kidney injury

Rapid glomerular disease, monoclonal protein toxicity, nephrotic thrombosis, infection or over-rapid diuresis can accompany proteinuria and cause an urgent fall in filtration.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Follow ACR and eGFR at the NICE frequency for the combined G/A category and after kidney-protective medicines, interpreting percentage change over adequate intervals.
Check creatinine and potassium before and one to two weeks after ACE inhibitor or ARB initiation or dose escalation, then respond to the size and stability of change.
In nephrotic syndrome, monitor weight, oedema, orthostatic blood pressure, albumin, renal function and symptoms of infection or thrombosis while treatment evolves.
For diabetes, align ACR with HbA1c, retinal and neuropathy review but investigate discordant rapid decline or active urine rather than accepting an automatic diabetic label.
After apparent remission, continue surveillance because ACR recurrence can precede eGFR decline and may signal relapse, poor adherence or renewed systemic disease.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Albuminuria can define CKD

Persistent A2 or A3 is kidney damage even when eGFR exceeds 60. The G category alone would miss both diagnosis and excess cardiovascular risk.

ACR and PCR answer different questions

ACR is sensitive for glomerular albumin leakage; PCR captures all measured protein. Their discordance can be the clue to tubular or monoclonal overflow disease.

Oedema does not equal safe diuresis

Some nephrotic patients have low effective circulating volume despite total-body sodium excess. Orthostasis, kidney function and treatment response must guide the pace.

Transient does not mean imaginary

Exercise, infection and fever can genuinely raise albumin excretion. Repeating under stable conditions separates reversible stress from persistent kidney damage.

Protein fall can mislead

ACR may fall when filtration collapses or RAAS therapy reduces pressure. Interpret it with eGFR, albumin and clinical state before declaring disease remission.

11Common pitfallsFrequent interpretation and management errors.

01
Using reagent-strip protein as the quantitative CKD albuminuria category.
02
Failing to repeat a stable ACR between 3 and 70 mg/mmol on an early-morning sample.
03
Excluding paraprotein kidney disease because dipstick albumin is weak or absent.
04
Calling abrupt nephrotic syndrome diabetic nephropathy without checking time course and sediment.
05
Starting RAAS blockade without baseline and follow-up potassium and creatinine.
06
Treating severe oedema with unmonitored rapid diuresis despite possible intravascular depletion.