Pathophysiology

Pathophysiology

P-II-30. Causes of abnormal urine color

尿色調異常の原因

Normal Urine Color

  • Straw yellow = physiological

Causes of Abnormal Color

  • Orange → concentrated urine, or drugs (e.g. rifampin)
  • Red → hematuria
  • Brick red → hemoglobin (hemoglobinuria) or myoglobin (myoglobinuria)
  • Beer-dark (brown) → conjugated bilirubin
  • Black → genetic disorders, melanoma
  • Foamy urine → proteinuria
  • Turbidity → cellular urine (pus, blood, crystals). Faint nubecula = Tamm-Horsfall protein (uromodulin)
  • Concentration: reflected in specific gravity (1.001–1.030), where 1.010 = isosthenuria (equal to plasma)

一問一答

▶What is the normal (physiological) colour of urine?

Straw yellow.

▶What causes orange-coloured urine?

Concentrated urine or certain drugs such as rifampin.

▶What does red-coloured urine indicate?

Hematuria (red blood cells in the urine).

▶What does brick-red urine suggest?

Haemoglobin (haemoglobinuria) or myoglobin (myoglobinuria).

▶What causes beer-dark (brown) urine?

Conjugated bilirubin in the urine.

▶What can cause black-coloured urine?

Certain genetic disorders and melanoma.

▶What does foamy urine indicate?

Proteinuria.

▶What does turbidity (cloudiness) of urine usually represent?

Cellular content — pus, blood, or crystals.

▶What is a faint nubecula in urine due to?

Tamm-Horsfall protein (uromodulin).

▶What is the normal range of urine specific gravity?

1.001–1.030.

▶What specific gravity defines isosthenuria?

1.010 — equal to plasma osmolality.

▶Why does concentrated urine appear darker/orange?

Less water dilutes the urinary pigments, intensifying the colour.

▶How can you distinguish haematuria from haemoglobinuria/myoglobinuria by colour alone?

Haematuria tends to be red, whereas free haemoglobin or myoglobin gives a brick-red colour (and requires microscopy/tests to confirm).

▶Why does conjugated bilirubin, but not unconjugated, appear in urine?

Conjugated bilirubin is water-soluble and can be excreted by the kidney, darkening the urine; unconjugated bilirubin is not.

▶Which antibiotic classically turns urine (and other secretions) orange-red?

Rifampin.

▶What does true turbidity distinguish from a harmless nubecula?

True turbidity reflects cells (pus, blood, crystals), while nubecula is only a faint protein cloud (uromodulin).

▶What urinary appearance points to proteinuria rather than colour change?

Persistent foam (foamy urine).

▶What does specific gravity measure about the urine?

Its concentration (the kidney's ability to concentrate or dilute urine).

▶Which two pigments cause a brick-red urine and where do they come from?

Haemoglobin (from intravascular haemolysis) and myoglobin (from muscle breakdown/rhabdomyolysis).

▶Why is urine colour a useful but non-specific diagnostic clue?

Colour suggests categories (blood, pigments, bilirubin, drugs) but confirmation needs dipstick, microscopy, or lab tests.