Urobilinogen

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The urobilinogen test detects impaired liver function by measuring urine levels of urobilinogen, the colorless, water-soluble product that results from the reduction of bilirubin by intestinal bacteria. Absent or altered urobilinogen levels can indicate hepatic damage or dysfunction. Increased urine urobilinogen levels may indicate hemolysis of red blood cells.

Urobilinogen is a byproduct of hemoglobin breakdown. It is produced in the intestinal tract as a result of the action of bacteria on bilirubin. Almost half of the urobilinogen produced recirculates through the liver and then returns to the intestines through the bile duct. Urobilinogen is then excreted in the feces where it is converted to urobilin. As the urobilinogen circulates in the blood to the liver, a portion of it is diverted to the kidneys and appears as urinary urobilinogen. Up to 1 mg/dL or Ehrlich unit of urobilinogen is present in normal urine. A result of 2.0 mg/dL represents the transition from normal to abnormal and the patient should be evaluated further. It is important to note that the reagent strip cannot determine the absence of urobilinogen.

The test for urobilnogen is based on the Ehrlich Aldehyde Reaction. P-dimethylaminobenzaldehyde in an acid medium with a color enhancer reacts with urobilinogen to form a pink-red color. The strip reactivity increases with increasing temperature. The optimum temperature for testing is 22° - 26°C. A freshly voided sample is best for optimal results.

A false positive urobilinogen reaction may occur with the dipstick method when substances known to react with Ehrlich's reagent such as sulfonamides and p-aminosalicylic acid are present in the urine. Drugs that contain Azo dyes, such as Azo Gantrisin®, have a gold color that masks the reaction, causing a false positive reaction. Atypical color reactions may be obtained in the presence of high concentrations of p-aminobenzoic acid. The dipstick urobilinogen test cannot detect porphobilinogen in a urine specimen. Porphobilinogen is a molecule formed during the synthesis of the heme portion of hemoglobin.

Due to the instability of urobilinogen, a false negative result may occur using a dipstick method if the urine specimen has remained at room temperature for an extended period of time in the light. A false negative result may also occur if formalin is present.

Test results that are 2.0 Ehrlich units or greater can be confirmed using the Watson-Schwartz qualitative test. This test will differentiate between urobilinogen and porphobilinogen.

Test results
An increased urobilinogen concentration in urine is a sensitive index of liver dysfunction or hemolytic disorders. Urobilinogenuria is caused by e. g. virus hepatitis, chronic hepatitis, liver cirrhosis, infections, poisonings, congestion or carcinoma of liver, hemolytic, and pernicious anemina, polycythemia and pathological state of the intestinal tract with an increased resorbence.
Increased urobilinogen values may indicative of:
·overburdening of the liver  
·excessive RBC breakdown  
·increased urobilinogen production  
·re-absorption - a large hematoma  
·restricted liver function  
·hepatic infection  
·poisoning  
·liver cirrhosis  
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.
Low urobilinogen values may indicative of:
·failure of bile production  
·obstruction of bile passage  
Medications that may decrease urobilinogen level: Para-aminosalicylic acid, phenazopyridine, procaine, phenothiazines, and sulfonamides.

Also you should know
The urobilinogen remaining in the intestine (stercobilinogen) is oxidized to brown stercobilin, which gives the feces their characteristic color.

Urinary urobilinogen may be increased in the presence of a hemolytic process such as hemolytic anemia. It may also be increased with infectious hepatitis, or with cirrhosis. Comparing the urinary bilirubin result with the urobilinogen result may assist in distinguishing between red cell hemolysis, hepatic disorder, and biliary obstruction. Urobilinogen is increased in hemolytic disorder and urine bilirubin is negative. Urobilinogen is increased in hepatic disorder, and urine bilirubin may be positive or negative. Urobilinogen is low with biliary obstruction, and urine bilirubin is positive. Reagent strips methods however, cannot distinguish normal urobilinogen from absent urobilinogen, as might be seen in complete biliary obstruction.


 
 
 
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All information on this page is intended for your general knowledge only and does not provide medical advice, diagnosis or treatment.