Urine color is an important indicator of health and disease. The pigments that give urine its yellowish hue are called urochromes. Urochromes are breakdown products of hemoglobin from old red blood cells. Bilirubin, a breakdown product of heme, is the primary urochrome that gives urine its characteristic color.
Urochromes
The main urochromes that contribute to urine color include:
- Bilirubin – a yellowish pigment formed by the breakdown of heme in red blood cells
- Urobilin – a colorless precursor to bilirubin formed in the intestines
- Urobilinogen – a colorless compound that is converted to urobilin
- Stercobilin/stercobilinogen – orange or red pigments formed from bilirubin breakdown in the intestines
In healthy individuals, around 200-250 mg of bilirubin is excreted in urine per day. An increase or decrease in bilirubin excretion will cause the urine color to become darker or lighter.
What gives urine its yellow color?
The yellow color of normal urine is primarily due to urochrome pigments, mainly bilirubin. Here are some key facts about why urine is yellow:
- Bilirubin is a breakdown product of heme from the destruction of old red blood cells in the spleen.
- The liver converts bilirubin into a water-soluble form called urobilinogen that is excreted into the intestines.
- Some urobilinogen is reabsorbed and converted back into urobilin in the kidneys, then excreted into urine.
- Higher concentrations of urobilin and bilirubin lead to a darker yellow urine color.
- Colorless urochrome precursors are converted into yellow urochromes by the acidic environment in the kidneys.
In short, old red blood cells are broken down into bilirubin, which is processed by the liver and kidneys into yellow urochrome pigments that end up in urine. The more concentrated the urochromes, the darker the yellow color.
What causes urine color to vary?
Many factors can affect the concentration and composition of urochromes, leading to variations in urine color. Common causes include:
- Hydration – More dilute urine is lighter yellow while concentrated urine is darker.
- Diet – Foods like carrots, vitamin supplements, and blackberries can darken urine.
- Medications – Drugs like AZO can turn urine orange or red.
- Liver disease – Increased bilirubin turns urine dark amber.
- Kidney disease – Causes impaired urochrome excretion.
- Infection – Byproducts from bacteria can change color.
- Food dyes – Artificial food coloring passes into urine.
Underlying health conditions like jaundice, gallstones, liver disease, and kidney disorders can also alter bilirubin and urochrome levels, significantly changing urine hue.
Normal urine color chart
This chart shows the spectrum of normal urine colors and their common causes:
| Urine Color | Color Description | Common Causes |
|---|---|---|
| Pale straw | Very diluted urine | Excess hydration, diuretics, diabetes insipidus |
| Straw yellow | Diluted, normal urine | Normal hydration |
| Gold | Darker yellow urine | Concentrated urine, B-vitamins |
| Amber | Dark yellow to orange urine | Concentrated urine, AZO medication |
Urine color can vary from pale yellow to dark amber and still be considered normal. But very pale or dark urine can signify underlying conditions that need medical attention.
Abnormal urine colors
Unusual urine colors can be caused by medical conditions, foods, dyes, and medications. Here are some abnormal urine colors and their typical causes:
- Orange: Dehydration, AZO medication, jaundice
- Pink: Blood, kidney disease, UTI, cancer medications
- Red: Hematuria, kidney stones, UTIs, laxative abuse
- Blue: Rare genetic conditions, methylene blue medication
- Green: Diet, medications, Pseudomonas infection
- Brown: Liver disease, severe dehydration, rhabdomyolysis
- Black/gray: Alcaptonuria, melanoma medications, urinary stones
Seeing any of these unusual urine hues can be a sign of an underlying medical condition and should prompt seeing a healthcare provider.
When to see a doctor about urine color
Consult a physician if you experience:
- Very pale urine that persists – may indicate diabetes, kidney disease, or liver failure
- Dark brown urine – can signal liver disease or rhabdomyolysis
- Pink, red, or cola-colored urine – indicates blood, which can signify UTI, kidney stones, or cancer
- Orange urine and yellow eyes/skin – suggests jaundice from liver disease or gallstones
- Blue or green urine – caused by rare genetic diseases or food dyes/medications
- Foul-smelling or cloudy urine – associated with dehydration and UTIs
- Changes in urine color that last over 48 hours – needs evaluation to determine the cause
Tracking the color of your urine is a simple way to monitor your health day-to-day. But if you notice unusual or concerning changes in urine color, seek medical advice to address any underlying condition.
Conclusion
In summary, the main pigments that give urine its yellowish color are called urochromes. Bilirubin from the breakdown of red blood cells is the primary urochrome responsible for the typical yellow hue. Urine color normally ranges from pale yellow to deep amber based on the concentration of these pigments. But abnormal urine colors like brown, blue, red, or green can signify an underlying illness. Seeing a physician is recommended if urine color changes persist for over 48 hours or indicate a possible medical issue.