Urobilinogen is a colorless by-product of bilirubin reduction. It is formed in the intestines by
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
l action on bilirubin. About half of the urobilinogen formed is reabsorbed and taken up via the portal vein to the liver, enters circulation and is excreted by the kidney.
Increased amounts of bilirubin are formed in
hemolysis
Hemolysis or haemolysis (), also known by several other names, is the rupturing ( lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in vivo ...
, which generates increased urobilinogen in the gut. In liver disease (such as
hepatitis
Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes ( jaundice), poor appetite, vomiting, tiredness, abdominal ...
), the intrahepatic urobilinogen cycle is inhibited also increasing urobilinogen levels. Urobilinogen is converted to the yellow pigmented
urobilin
Urobilin or urochrome is the chemical primarily responsible for the yellow color of urine. It is a linear tetrapyrrole compound that, along with the related colorless compound urobilinogen, are degradation products of the cyclic tetrapyrrole heme ...
apparent in urine.
The urobilinogen in the intestine is directly reduced to brownish colour
stercobilin
Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: A cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. Kay IT, Weimer M, Watson CJ (1963)â ...
, which gives the feces their characteristic color. It can also be reduced to
stercobilinogen
Stercobilinogen (fecal urobilinogen) is a chemical created by bacteria in the gut. It is made of broken-down hemoglobin. It is further processed to become the chemical that gives feces its brown color.jaundice or treatment with
broad-spectrum antibiotics
A broad-spectrum antibiotic is an antibiotic that acts on the two major bacterial groups, Gram-positive and Gram-negative, or any antibiotic that acts against a wide range of disease-causing bacteria. These medications are used when a bacterial i ...
, which destroy the intestinal bacterial flora. (Obstruction of bilirubin passage into the gut or failure of urobilinogen production in the gut.)
Low urine urobilinogen levels may result from congenital enzymatic jaundice (hyperbilirubinemia syndromes) or from treatment with drugs that acidify urine, such as ammonium chloride or ascorbic acid.
Elevated levels may indicate
hemolytic anaemia
Hemolytic anemia or haemolytic anaemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular). This most commonly ...
(excessive breakdown of red blood cells RBC), overburdening of the liver, increased urobilinogen production, re-absorption – a large hematoma, restricted liver function, hepatic infection, poisoning or liver cirrhosis.
Nomenclature
Urobilinogen ( D-urobilinogen) is closely related to two other compounds: mesobilirubinogen (a.k.a. I-urobilinogen) and stercobilinogen (a.k.a. L-urobilinogen). Specifically, urobilinogen can be reduced to form mesobilirubinogen, and mesobilirubinogen can be further reduced to form stercobilinogen. Confusingly, however, all three of these compounds are frequently collectively referred to as "urobilinogens".
Measurement
Urobilinogen content is determined by a reaction with Ehrlich's reagent, which contains para-Dimethylaminobenzaldehyde and may be measured in ''Ehrlich units''. Ehrlich's reagent reacts with urobilinogen to give a pink-red color. One Ehrlich unit is equal to one milligram of urobilinogen per deciliter of sample (1 mg/dL).Urobilinogenfrom Information and Courses MediaLab, Inc. Retrieved on Jan 8, 2009