Urobilinogen (UBG, URO)
2 types of bile pigment may be present in the urine, bilirubin and urobilinogen.
Small amounts of bilirubin may be present in the urine of healthy individuals which are not detected by standard laboratory tests. Therefore, it is generally assumed that no bilirubin is present in the urine of healthy individuals. The condition in which high levels of bilirubin are detected in the urine is called bilirubinuria.
Bilirubin changes the color of urine making it dark.
Bilirubin is produced as a breakdown product of erythrocytes. It is not soluble in water – this is the so called unconjugated bilirubin which cannot get through the kidney filter. This is why it is not detected in the urine even if there are high levels of it in the blood. However, the unconjugated bilirubin is sent to the liver which conjugates the bilirubin with glucuronic acid, making it soluble in water. This is why it is then expelled from the body during urination. This conjugated bilirubin goes into the bile and out into the gastrointestinal tract.
If there are high concentrations of conjugated bilirubin in the blood, the kidneys begin producing it and it enters the urine. The presence of bilirubin in the urine occurs mostly due to liver diseases and bile duct obstruction.
Small amounts of urobilinogen are normally found in the freshly voided urine of a healthy individual which, if the urine is allowed to stand for long periods of time, oxidizes and transforms into urobilin. Urobilinogen is colorless, while urobilin is yellow. This is why urobilin-rich urine becomes darker if allowed to stand for long periods of time.
The condition in which excessive amounts of urobilin are present in the urine is called urobilinogenuria.
Urobilinogen is generated from bilirubin by enzymes, bacteria and cells of the lining of intestines which enter the bowels through the bile.
In healthy individuals, urobilinogen is produced at a certain rate and is expelled from the body with feces and in small amounts with urine. Various diseases may enhance the production of urobilinogen causing its excessive clearance from the body; or urobilinogen production may decrease and urobilinogen will not be found in the urine.
Elevated levels of urobilinogen are seen in all diseases causing an intensive decay of erythrocytes as the released hemoglobin is used to produce excessive amounts of bilirubin and then urobilinogen.
Urobilinogen in the urine may be caused by the following diseases: malaria, hemolytic jaundice, internal bleeding (gastrointestinal tract, lungs, female genital organs).