Medicine – Causes of Proteinuria

Proteinuria means an abnormal amount of protein in the urine. It may be temporary and benign, or it may indicate significant renal disease. The causes are most usefully understood according to whether the proteinuria is transient, glomerular, tubular, overflow, or post-renal.

1. Infection and Febrile Illness

The original notes correctly include:

Fever.

Acute febrile illness can cause:

Transient proteinuria.

This usually resolves once the acute illness settles.

Therefore, a small amount of protein detected during fever does not automatically indicate chronic kidney disease.

2. Urinary Tract Infection

A UTI can produce mild proteinuria because inflammation within the urinary tract allows protein and inflammatory material to enter the urine.

It is often associated with:

Pyuria.

Bacteriuria.

Dysuria.

Frequency.

Proteinuria from uncomplicated UTI is usually:

Mild rather than nephrotic-range.

3. Chronic Pyelonephritis

Chronic pyelonephritis and chronic tubulointerstitial scarring can cause:

Persistent low-grade proteinuria.

Because the main pathology affects:

Tubules and interstitium,

the amount of protein is usually less than in major glomerular disease.

4. Renal Tuberculosis

Genitourinary tuberculosis can cause:

Proteinuria.

However, its more characteristic urinary finding is:

Persistent sterile pyuria.

Microscopic haematuria may also occur.

Therefore:

RENAL TB → THINK STERILE PYURIA MORE THAN HEAVY PROTEINURIA.

5. Glomerular Disease

Glomerular disease is the major cause of:

Moderate to heavy proteinuria.

Damage to the glomerular filtration barrier allows excessive plasma proteins, especially:

Albumin,

to enter the urine.

6. Diabetes Mellitus

The original notes correctly include:

Diabetes mellitus.

Diabetic kidney disease causes:

Glomerular hyperfiltration.

GBM thickening.

Mesangial expansion.

Intraglomerular hypertension.

These changes lead to increasing urinary albumin loss.

7. Proteinuria in Diabetic Kidney Disease

The traditional sequence is:

Normal albumin excretion

↓

Moderately increased albuminuria

↓

Severely increased albuminuria

↓

Heavy proteinuria

↓

Progressive CKD.

However, some patients can develop declining GFR without marked albuminuria.

8. Hypertension

Long-standing hypertension can cause:

Hypertensive nephrosclerosis.

This may produce:

Persistent proteinuria.

Usually the amount is:

Low to moderate.

If proteinuria is very heavy, another glomerular cause should be considered.

9. Pre-Eclampsia

The original notes include:

Pre-eclampsia.

Pre-eclampsia occurs after approximately:

20 weeks of pregnancy

and causes:

Hypertension with maternal organ dysfunction.

Proteinuria is common.

10. Mechanism in Pre-Eclampsia

The renal lesion classically involves:

Glomerular endotheliosis.

This increases glomerular permeability and produces:

Proteinuria.

In severe disease, proteinuria may become:

Nephrotic-range.

11. Acute Glomerulonephritis

Acute GN may cause:

Proteinuria.

However, the classic nephritic pattern also includes:

Haematuria.

Dysmorphic RBCs.

RBC casts.

Hypertension.

Reduced GFR.

Proteinuria is usually less marked than in nephrotic syndrome, though overlap can occur.

12. Chronic Glomerulonephritis

Chronic GN may cause:

Persistent proteinuria

with gradual progression to:

Chronic kidney disease.

The quantity depends on the underlying glomerular lesion.

13. Nephrotic Syndrome

The original notes list:

Nephrotic syndrome.

This is not a single disease, but a clinical syndrome characterised by:

Heavy proteinuria.

Hypoalbuminaemia.

Generalised oedema.

Hyperlipidaemia.

14. Common Causes of Nephrotic-Range Proteinuria

Important causes include:

Minimal change disease.

FSGS.

Membranous nephropathy.

Diabetic kidney disease.

Amyloidosis.

Membranous lupus nephritis.

15. Neoplastic Causes

The original notes include:

Renal tract tumour

and

Multiple myeloma.

These cause proteinuria through very different mechanisms.

16. Renal Tract Tumour

Tumours of the kidney or urinary tract may cause protein to appear in urine because of:

Bleeding.

Inflammation.

Parenchymal disruption.

However, the more characteristic finding is:

Haematuria.

Marked isolated proteinuria is not usually the main presentation.

17. Multiple Myeloma

Multiple myeloma can produce:

Overflow proteinuria.

This occurs because large quantities of monoclonal:

Free light chains

are produced and filtered by the kidney.

18. Bence Jones Protein

The older term:

Bence Jones protein

refers to urinary monoclonal free light chains.

Modern assessment commonly uses:

Serum free light chains.

Serum immunofixation.

Urine studies when indicated.

19. Important Dipstick Limitation in Myeloma

Standard urine dipsticks detect mainly:

Albumin.

Therefore a patient with large amounts of:

Light-chain proteinuria

may have substantial total urinary protein despite only modest dipstick positivity.

This is an important clue to:

Paraprotein-related kidney disease.

20. Acute Tubular Injury

The original notes include:

ATN, more accurately often termed:

Acute tubular injury – ATI.

Tubular injury can cause:

Tubular proteinuria.

21. Mechanism of Tubular Proteinuria

Normally, small low-molecular-weight proteins are filtered and then reabsorbed by:

Proximal tubular cells.

When tubular function is damaged, reabsorption falls.

Therefore these proteins remain in the urine.

22. Amount of Protein in Tubular Disease

Tubular proteinuria is usually:

Mild to moderate.

It is generally less severe than:

Glomerular proteinuria.

Therefore nephrotic-range proteinuria should usually suggest:

A glomerular process.

23. Acute Interstitial Nephritis

Acute interstitial nephritis can cause:

Mild-to-moderate proteinuria.

It is often associated with:

Sterile pyuria.

WBC casts.

Microscopic haematuria.

AKI.

24. NSAID-Associated AIN

An important exception is:

NSAID-related acute interstitial nephritis.

This can occasionally cause:

Heavy or nephrotic-range proteinuria,

especially when associated with:

Minimal-change-like glomerular injury.

25. Transient Proteinuria

An important category missing from the original list is:

Transient proteinuria.

Possible causes include:

Fever.

Strenuous exercise.

Acute illness.

Seizures.

Severe physiological stress.

It usually resolves when the trigger disappears.

26. Orthostatic Proteinuria

Another important benign cause is:

Orthostatic proteinuria.

This occurs mainly in:

Adolescents and young adults.

Protein appears when the patient is upright but falls or disappears during:

Overnight recumbency.

27. Orthostatic Pattern

A typical pattern is:

Daytime urine → protein present.

First-morning urine → normal or minimal protein.

This is generally benign.

28. Glomerular Proteinuria

Glomerular proteinuria occurs when the filtration barrier becomes abnormally permeable.

The dominant urinary protein is usually:

Albumin.

Important causes include:

Diabetes.

Primary GN.

Secondary GN.

Nephrotic syndromes.

Pre-eclampsia.

29. Tubular Proteinuria

Tubular proteinuria results from impaired proximal tubular reabsorption.

Causes include:

Acute tubular injury.

Acute interstitial nephritis.

Chronic tubulointerstitial disease.

30. Overflow Proteinuria

Overflow proteinuria occurs when excessive amounts of small proteins circulate in plasma and overwhelm tubular reabsorption.

The classic cause is:

Multiple myeloma.

Other examples include:

Myoglobin in rhabdomyolysis.

Haemoglobin in intravascular haemolysis.

31. Post-Renal Proteinuria

Protein can also enter urine from inflammation or bleeding after it has left the glomerulus.

This is called:

Post-renal proteinuria.

Examples include:

UTI.

Urinary tract inflammation.

Tumours.

Bleeding.

This usually produces relatively modest proteinuria.

32. Proteinuria and Amyloidosis

An important cause not listed originally is:

Amyloidosis.

Amyloid deposition in the glomeruli can cause:

Heavy proteinuria

and

Nephrotic syndrome.

This is particularly important in:

AL amyloidosis

and

AA amyloidosis.

33. Proteinuria and SLE

Systemic lupus erythematosus can cause:

Lupus nephritis.

Proteinuria may occur in several lupus nephritis classes.

A particularly strong nephrotic association is:

Class V membranous lupus nephritis.

34. Measuring Proteinuria

Modern assessment usually uses a spot urine:

Albumin:creatinine ratio – ACR

for albuminuria.

A:

Protein:creatinine ratio – PCR

may be useful when total protein is more relevant.

35. ACR Categories

Albuminuria is commonly classified as:

A1 – normal to mildly increased.

A2 – moderately increased.

A3 – severely increased.

Interpretation should always be combined with:

eGFR

and

clinical context.

36. Confirm Persistent Proteinuria

A single positive urine result does not necessarily indicate chronic kidney disease.

Proteinuria may be transient because of:

Fever.

Exercise.

UTI.

Acute illness.

Therefore persistent proteinuria usually requires:

Repeat testing.

37. First-Morning Urine

A:

First-morning urine sample

is useful because it reduces the effects of:

Posture.

Exercise.

Daytime activity.

It is especially useful when considering:

Orthostatic proteinuria.

38. Proteinuria with Haematuria

The combination:

Proteinuria + haematuria

raises concern for:

Glomerular disease.

This is particularly important when associated with:

Dysmorphic RBCs.

RBC casts.

Reduced renal function.

Hypertension.

39. Proteinuria with Oedema

Heavy urinary protein loss causes:

Hypoalbuminaemia.

This lowers plasma oncotic pressure and contributes to:

Generalised oedema.

Therefore:

HEAVY PROTEINURIA + HYPOALBUMINAEMIA + OEDEMA → THINK NEPHROTIC SYNDROME.

40. Proteinuria with Diabetes

In diabetes, persistent albuminuria may indicate:

Diabetic kidney disease.

However, consider another diagnosis if there is:

Rapid renal deterioration.

Active urine sediment.

Marked haematuria.

Abrupt heavy proteinuria.

41. Proteinuria with Myeloma Features

Think of myeloma when proteinuria occurs with:

Anaemia.

Bone pain.

Hypercalcaemia.

Renal dysfunction.

Monoclonal protein abnormalities.

42. Infection Causes – Note Form

Fever:

Transient proteinuria.

Usually resolves when illness settles.

UTI:

Usually mild post-renal proteinuria.

Often accompanied by pyuria and bacteriuria.

Chronic pyelonephritis:

Usually low-grade proteinuria from tubulointerstitial scarring.

Renal TB:

Can cause proteinuria, but sterile pyuria is more characteristic.

43. Glomerular Causes – Note Form

Diabetes:

Major cause of persistent albuminuria.

May progress to nephrotic-range proteinuria.

Hypertension:

Usually low-to-moderate proteinuria.

Very heavy proteinuria suggests another glomerular disorder.

Pre-eclampsia:

Proteinuria due to glomerular endotheliosis.

Acute and chronic GN:

Proteinuria often with haematuria and RBC casts.

Nephrotic syndrome:

Heavy proteinuria with hypoalbuminaemia and oedema.

44. Neoplastic Causes – Note Form

Renal tract tumour:

Can cause proteinuria through bleeding or local tissue injury.

Haematuria is more characteristic.

Multiple myeloma:

Overflow proteinuria due to monoclonal free light chains.

45. Tubular Causes – Note Form

Acute tubular injury:

Impaired reabsorption of low-molecular-weight proteins.

Usually mild-to-moderate proteinuria.

Acute interstitial nephritis:

Mild-to-moderate proteinuria.

Often with sterile pyuria and WBC casts.

46. Important Additions

Other important causes include:

Orthostatic proteinuria.

Exercise-induced transient proteinuria.

Amyloidosis.

Lupus nephritis.

Minimal change disease.

FSGS.

Membranous nephropathy.

Rhabdomyolysis-related myoglobinuria.

47. Important Corrections to the Original Notes

Nephrotic syndrome is not itself a single disease.

It is a:

CLINICAL SYNDROME CAUSED BY UNDERLYING GLOMERULAR DISORDERS.

Hypertension generally causes:

LOW-TO-MODERATE PROTEINURIA.

Marked nephrotic-range proteinuria should prompt consideration of:

ANOTHER GLOMERULAR DISEASE.

Renal tract tumours more classically cause:

HAEMATURIA

than heavy proteinuria.

Renal TB is more classically associated with:

STERILE PYURIA.

ATN/ATI and interstitial nephritis usually cause:

TUBULAR, GENERALLY NON-NEPHROTIC PROTEINURIA.

Key Clinical Pattern

Think of proteinuria by mechanism:

GLOMERULAR → ALBUMIN LEAK.

Examples:

DIABETES + GN + NEPHROTIC DISEASE + PRE-ECLAMPSIA.

TUBULAR → FAILURE TO REABSORB SMALL PROTEINS.

Examples:

ATI/ATN + INTERSTITIAL NEPHRITIS.

OVERFLOW → TOO MUCH SMALL PROTEIN IN THE BLOOD.

Classic example:

MYELOMA LIGHT CHAINS.

POST-RENAL → PROTEIN ENTERS URINE FROM THE URINARY TRACT.

Examples:

UTI + TUMOUR + BLEEDING.

And remember:

HEAVY PROTEINURIA + OEDEMA + HYPOALBUMINAEMIA → NEPHROTIC SYNDROME.

PROTEINURIA + HAEMATURIA + RBC CASTS → THINK GLOMERULONEPHRITIS.