Urobilin (UB)

Urobilin is a yellow biochemical linear tetrapyrrole compound. Urobilin and its related compound, urobilinogen, are degradation products of the cyclic tetrapyrrole heme, and is primarily responsible for the yellow color of urine. Urobilin is generated from the degradation of heme, which is first degraded through biliverdin to bilirubin. Bilirubin is then excreted as bile, which is further degraded by microbes present in the large intestine to urobilinogen, and reabsorbed into the bloodstream, where it is converted into urobilin and eventually excreted by the kidneys. Many urine tests (urinalysis) monitor the amount of urobilin in urine, as its levels can give insight on the effectiveness of urinary tract function. Normally, urine would appear as either light yellow urine or colorless. A lack of water intake, for example following sleep or dehydration, reduces the water content of urine, thereby concentrating urobilin and producing a darker color of urine.