Urobilinogen is a colorless by-product of
bilirubin
Bilirubin (BR) ( Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from t ...
reduction. It is formed in the intestines by
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
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 viv ...
, 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 apparent in urine.
The urobilinogen in the intestine is directly reduced to brownish colour
stercobilin, which gives the feces their characteristic color. It can also be reduced to
stercobilinogen, which can then be further oxidized to stercobilin.
In biliary obstruction, below-normal amounts of conjugated bilirubin reach the intestine for conversion to urobilinogen. With limited urobilinogen available for reabsorption and excretion, the amount of urobilin found in the urine is low. High amounts of the soluble conjugated bilirubin enter the circulation where they are excreted via the kidneys. These mechanisms are responsible for the dark urine and pale stools observed in biliary obstruction.
Low urine urobilinogen may result from complete obstructive
jaundice or treatment with
broad-spectrum antibiotics, 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
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...
.
Elevated levels may indicate
hemolytic anaemia (excessive breakdown of red blood cells RBC), overburdening of the liver, increased urobilinogen production, re-absorption – a large
hematoma
A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...
, 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
See also
* Urobilin
References
External links
Biochemicals pathways Map
{{Heme metabolism intermediates
Tetrapyrroles
Hepatology