Why is urine yellow in color?
Although urine is straw yellow in color, the shades can vary without being due to any abnormality or disease process. Urine is a collection of water, waste products and excess compounds in the body. It’s characteristic color is due mainly to the presence of urobilins (urochrome). These urobilins are a group of related compounds that are formed during the breakdown of red blood cells, particularly hemoglobin. Although most of these compounds are passed out with the bile into the gut and then expelled with the feces, some of urobilinogen is broken down by intestinal bacteria to form urobilins which are reabsorbed and then excreted in the urine.
Darker yellow colored urine
A darker yellow colored urine is often seen when a person is exposed to hot weather and does not drink sufficient fluids. In an attempt to conserve the body’s fluids during dehydration, the kidney reabsorbs water in the kidney thereby concentrating it. In these instances, the urine may appear a more mustard or amber yellow in color. However, it may also indicate a problem with bile secretion if the darker colored urine is accompanied by pale stools.
Dark urine, however, that is bordering on brown in color is abnormal. Although the urine is darker yellow in color, it should be clear or translucent. Murky urine is due to various other causes like pus or mucus in the urine and is discussed further under cloudy urine
Causes of Dark Urine
Certain medication, supplements, foods and beverages may cause a dark urine. The color of the urine should restore to normal once these compounds are removed from the body and not reintroduced into the system.
- Senna in laxatives
- Excessive consumption of B-complex vitamins
- Drugs like phenazopyridine, methyldopa and statins
- Food colorants (dyes)
- Strenuous exercise
- Dehydration – hot weather, after excessive alcohol consumption
Although dark colored urine is a known side effect of certain drugs, it should still be investigated by a doctor to exclude adverse drug reactions or other underlying conditions.
Pathological causes of dark urine includes :
- Liver diseases like hepatitis and cirrrhosis
- Obstructive jaundice
- Bile duct stones
- Hemolytic anemia
- Paroxysmal nocturnal hemoglobinuria (rare) may cause dark urine in the morning upon waking
- Pancreas diseases
- Kidney diseases
- Kidney stones
- Urinary tract infection
- Mild hematuria (blood in urine)
- Copper poisoning
Other signs and symptoms, even if unrelated to the kidneys and urinary tract, may be an indication of a pathological cause of dark urine.
Article reviewed by Dr. Greg. Last updated on February 21, 2011