|Molar mass||592.726 (g/mol)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Urobilinogen is a colourless by-product of bilirubin reduction. It is formed in the intestines by bacterial action on bilirubin. About half urobilinogen is reabsorbed, taken up, via the portal vein, into circulation through the liver and excreted by the kidney.
Increased amounts of bilirubin are formed in hemolysis, which generates increased urobilinogen in the gut. In liver disease (such as hepatitis), 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 brown stercobilin, which gives the feces their characteristic color. It can also be reduced to stercobilinogen, which can then be further oxidized to stercobilin. This constitutes the normal "enterohepatic urobilinogen cycle".
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.)
Elevated levels may indicate hemolytic anaemia (excessive breakdown of red blood cells), overburdening of the liver, increased urobilinogen production, re-absorption - a large hematoma, restricted liver function, hepatic infection, poisoning or liver cirrhosis.
Urobilinogen (aka D-urobilinogen) is closely related to two other compounds: mesobilirubinogen (aka I-urobilinogen) and stercobilinogen (aka 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".
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 colour. For best results the Ehrlich's test 22-26 degrees Celsius because of the reactivity of the strip at higher temperatures. One Ehrlich unit is equal to one milligram of urobilinogen per deciliter of sample (1 mg/dL).
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- "Biochemical Pathways Map No. L5 L6". ExPASy Bioinformatics Resource Portal. Retrieved 12 December 2011.
- Henry's clinical diagnosis and management by laboratory methods. (22nd ed. ed.). Philadelphia, PA: Elsevier/Saunders. p. 543. ISBN 978-1-4377-0974-2.
- Urobilinogen Information and Courses from MediaLab, Inc. Retrieved on Jan 8, 2009