Medicine – Causes of Coloured Urine

Abnormal urine colour can result from blood, pigments, bilirubin, medications, foods, metabolic disorders or muscle breakdown. The colour itself may provide a useful diagnostic clue, but it should always be interpreted together with urinalysis, microscopy and the clinical context.

A practical way to approach coloured urine is to ask whether the colour is due to:

Blood.

Bilirubin.

Myoglobin.

Drugs or food pigments.

Metabolic pigments.

1. Haematuria

Haematuria means the presence of red blood cells in the urine.

Urine may appear:

Pink.

Red.

Brown.

Tea-coloured or cola-coloured.

The appearance depends on the amount and source of bleeding.

2. Glomerular Haematuria

When bleeding originates from the glomeruli, urine may appear:

Tea-coloured or cola-coloured.

This occurs because red blood cells become altered while passing through the nephron.

Typical associated findings include:

Dysmorphic RBCs.

Red-cell casts.

Proteinuria.

This pattern suggests:

Glomerulonephritis.

3. Non-Glomerular Haematuria

Bleeding from the urinary tract may produce:

Bright red or pink urine.

Possible causes include:

UTI.

Renal or ureteric calculi.

Urinary tract tumour.

Trauma.

Prostatic disease.

Clots, when present, generally favour:

Non-glomerular urinary tract bleeding.

4. Obstructive Jaundice

The original notes correctly include:

Obstructive jaundice.

In biliary obstruction, conjugated bilirubin accumulates in the blood.

Because conjugated bilirubin is:

Water-soluble,

it can be excreted in urine.

This produces:

Dark brown or tea-coloured urine.

5. Bilirubinuria

Urinary bilirubin indicates:

Conjugated hyperbilirubinaemia.

It may occur in:

Extrahepatic biliary obstruction.

Cholestatic liver disease.

Hepatocellular disease with conjugated bilirubin elevation.

Therefore dark urine is not limited specifically to obstructive jaundice.

6. Obstructive Jaundice Pattern

A typical pattern is:

Dark urine.

Pale stools.

Jaundice.

Pruritus.

The dark urine results from:

Conjugated bilirubin excretion.

The pale stools result from reduced delivery of:

Bile pigments to the intestine.

7. Drugs

Many medications can alter urine colour without causing urinary tract disease.

The classic example in the original notes is:

Rifampicin.

8. Rifampicin

Rifampicin can cause an:

Orange-red discoloration

of body fluids, including:

Urine.

Tears.

Sweat.

Saliva.

This is usually harmless.

Therefore:

RIFAMPICIN → ORANGE/RED URINE.

9. Other Drug-Related Urine Colours

Other medications can also alter urine colour.

Examples include:

Phenazopyridine → orange urine.

Metronidazole → dark or reddish-brown urine in some patients.

Nitrofurantoin → brownish urine.

Some laxatives containing senna → reddish or brown urine.

The exact colour varies with the drug and concentration.

10. Myoglobinuria

Myoglobinuria occurs when large amounts of myoglobin are released from damaged skeletal muscle.

The classic cause is:

Rhabdomyolysis.

Urine may appear:

Dark brown, red-brown or cola-coloured.

11. Myoglobinuria and Dipstick Testing

Urine dipsticks detect the haem component of:

Haemoglobin and myoglobin

as well as intact RBCs.

Therefore myoglobinuria produces:

Positive dipstick for “blood”

but urine microscopy shows:

Few or no red blood cells.

This is an important diagnostic clue.

12. Rhabdomyolysis Pattern

Think of rhabdomyolysis when dark urine is associated with:

Muscle pain.

Muscle weakness.

Very high CK.

Hyperkalaemia.

AKI.

Therefore:

DARK URINE + POSITIVE BLOOD DIPSTICK + FEW/NO RBCs → THINK MYOGLOBINURIA.

13. Haemoglobinuria

Another important cause of dark urine is:

Haemoglobinuria.

This occurs during significant:

Intravascular haemolysis.

Like myoglobinuria, the urine dipstick is positive for blood but microscopy may show:

Few or no RBCs.

14. Distinguishing Haematuria from Pigmenturia

A useful pattern is:

Dipstick positive for blood + many RBCs on microscopy → haematuria.

Dipstick positive for blood + few/no RBCs → myoglobinuria or haemoglobinuria.

This is one of the most useful clinical distinctions in coloured urine.

15. Beetroot

Eating beetroot can cause:

Red or pink urine.

This is known as:

Beeturia.

It is benign and does not indicate haematuria.

16. Beeturia

Beeturia may be mistaken for:

Blood in the urine.

A urine dipstick and microscopy can clarify the difference.

In beeturia:

Red colour is present

but there are no corresponding urinary red cells.

17. Porphyria

Certain porphyrias can produce urine that becomes:

Red, reddish-brown or port-wine coloured.

The colour may become more obvious after the urine stands or is exposed to:

Light and air.

18. Acute Porphyrias

Acute hepatic porphyrias may present with:

Severe abdominal pain.

Neurological symptoms.

Autonomic disturbance.

Psychiatric symptoms.

The urine may darken because of increased:

Porphyrin precursors and porphyrin pigments.

19. Alkaptonuria

Alkaptonuria is a rare inherited disorder of tyrosine metabolism caused by deficiency of:

Homogentisate 1,2-dioxygenase.

This leads to accumulation of:

Homogentisic acid.

20. Urine in Alkaptonuria

Fresh urine may initially appear relatively normal.

When exposed to:

Air,

homogentisic acid oxidises and polymerises.

The urine gradually turns:

Dark brown or black.

Therefore:

ALKAPTONURIA → URINE DARKENS ON STANDING.

21. Other Features of Alkaptonuria

Over time, homogentisic acid deposits in connective tissues, producing:

Ochronosis.

Patients may develop:

Bluish-black pigmentation of cartilage.

Degenerative arthritis.

Spinal disease.

22. Dark Urine in Dehydration

An important common cause not listed originally is:

Concentrated urine from dehydration.

Urine becomes:

Dark yellow or amber.

This results from increased concentration of normal urinary pigments rather than pathological blood or bilirubin.

23. Cloudy or Milky Urine

Although not strictly “coloured” urine, urine may appear cloudy or milky because of:

Pyuria.

Crystals.

Phosphaturia.

Chyluria.

Therefore appearance alone is not enough to determine the cause.

24. Red or Pink Urine – Note Form

Haematuria:

UTI.

Calculi.

GN.

Tumour.

Trauma.

Beetroot:

Benign beeturia.

Rifampicin:

Orange-red discoloration.

Porphyria:

Red to reddish-brown urine.

May darken on standing.

25. Brown or Cola-Coloured Urine – Note Form

Glomerular haematuria:

Tea/cola-coloured urine.

Myoglobinuria:

Rhabdomyolysis.

Dipstick positive for blood with few/no RBCs.

Haemoglobinuria:

Intravascular haemolysis.

Dipstick positive with few/no RBCs.

Bilirubinuria:

Conjugated hyperbilirubinaemia.

Dark tea/brown urine.

26. Orange Urine – Note Form

Rifampicin:

Classic orange-red urine.

Phenazopyridine:

Orange urine.

Concentrated urine:

Dark yellow/orange appearance may occur with dehydration.

27. Black Urine – Note Form

Alkaptonuria:

Urine becomes dark brown/black after standing.

Some porphyrias may also produce very dark urine.

28. Important Corrections to the Original Notes

Obstructive jaundice causes dark urine because of:

CONJUGATED BILIRUBINURIA.

However, conjugated bilirubin can also appear in urine in other hepatobiliary disorders, so dark urine is not exclusive to mechanical obstruction.

Myoglobinuria should be distinguished from haematuria by:

DIPSTICK POSITIVE FOR BLOOD + FEW OR NO RBCs ON MICROSCOPY.

An important additional differential is:

HAEMOGLOBINURIA FROM INTRAVASCULAR HAEMOLYSIS.

It gives the same dipstick pattern as myoglobinuria.

Beetroot causes benign red urine and should not be confused with true haematuria.

Alkaptonuria classically causes:

URINE THAT DARKENS ON STANDING OR EXPOSURE TO AIR.

Key Clinical Pattern

Remember the colour associations:

RED/PINK → HAEMATURIA, BEETROOT, RIFAMPICIN.

TEA/COLA → GLOMERULAR HAEMATURIA, MYOGLOBIN, HAEMOGLOBIN.

DARK BROWN → CONJUGATED BILIRUBIN.

ORANGE-RED → RIFAMPICIN.

RED-BROWN/PORT-WINE → PORPHYRIA.

BLACK ON STANDING → ALKAPTONURIA.

And the most useful investigation clue is:

DIPSTICK “BLOOD” + RBCs ON MICROSCOPY → HAEMATURIA.

DIPSTICK “BLOOD” + FEW/NO RBCs → MYOGLOBINURIA OR HAEMOGLOBINURIA.