Urobilinogen in Urine: Definition of This Compound, Clinical Importance, Levels, Test and Evaluation

Bilirubin is a yellowish substance in the liver that helps break down red blood cells.

Urobilinogen is a tetrapyrrole chemical compound that is the parent compound of both stercobilin (the pigment responsible for the brown color of stool) and urobilin (the pigment responsible for the yellow color of urine).

Clinical importance of urobilinogen in urine

Urobilinogen is formed through microbial degradation of its parent compound bilirubin .

Urobilinogen is actually made through the breakdown of heme, the red pigment in hemoglobin, and red blood cells (red blood cells). Red blood cells have a lifespan of approximately 120 days.

When red blood cells have reached the end of their useful life, the cells are engulfed by macrophages and their components are recycled or eliminated.

Heme is broken down when the enzyme known as heme oxygenase opens the heme ring, which is found in the endoplasmic reticulum of macrophages.

The oxidation process produces the linear tetrapyrrole known as biliverdin along with ferric iron (Fe3 +) and carbon monoxide (CO).

In the next reaction, the enzyme known as biliverdin reductase reduces a second methylene group (located between rings III and IV of the porphyrin ring) and produces bilirubin.

Bilirubin is significantly less extensively conjugated than biliverdin. This reduction causes a change in the color of the biliverdin molecule from blue-green (vert or green for green) to yellow-red, which is the color of bilirubin (ruby or ruby ​​for red).

In plasma, practically all bilirubin is strongly bound to plasma proteins, mainly albumin, because it is only sparingly soluble in aqueous solutions at physiological pH.

In sinusoids, unconjugated bilirubin dissociates from albumin, enters liver cells through the cell membrane through non-ionic diffusion to the smooth endoplasmic reticulum.

In hepatocytes, bilirubin-UDP-glucuronyltransferase (bilirubin-UGT) adds 2 additional glucuronic acid molecules to bilirubin to produce the more water-soluble version of the molecule known as bilirubin diglucuronide.

Bilirubin diglucuronide is rapidly transferred across the canalicular membrane into the bile canaliculi, where it is then excreted as bile into the large intestine.

Bilirubin is further broken down (reduced) by microbes in the large intestine to form a colorless product known as urobilinogen.

The urobilinogen that remains in the colon can be reduced to stercobilinogen and finally oxidized to stercobilin, or it can be directly reduced to stercobilin.

Part of the urobilinogen produced by the intestinal bacteria is reabsorbed and re-enters the enterohepatic circulation. This reabsorbed urobilinogen is oxidized and converted to urobilin.

Urobilin is processed through the kidneys and then excreted in the urine, causing the urine to turn yellow.

Urobilinogen (also known as D-urobilinogen) is closely related to two other compounds: mesobilirubinogen (also known as I-urobilinogen) and stercobilinogen (also known as L-urobilinogen).

Specifically, urobilinogen can be reduced to form mesobilirubinogen, and mesobilirubinogen can be further reduced to form stercobilinogen.

Confusingly, these three compounds are often collectively referred to as “urobilinogens.” The urobilinogen content can be determined by a reaction with Ehrlich’s reagent, which contains para-dimethylaminobenzaldehyde.

Ehrlich’s reagent reacts with urobilinogen to give a pink-red color. Low urobilinogen in urine can be the result of complete obstructive jaundice or treatment with broad-spectrum antibiotics, which destroy the intestinal bacterial flora.

Concentration levels

Low levels of urobilinogen in the urine can also be the result of congenital enzyme jaundice (hyperbilirubinemia syndromes) or treatment with drugs that acidify the urine, such as ammonium chloride or ascorbic acid.

Elevated levels of urinobilinogen in the urine may indicate hemolytic anemia , a large hematoma, restricted liver function, liver infection, liver poisoning or cirrhosis that destroy the intestinal bacterial flora.

Low levels of urobilinogen in the urine can also be the result of congenital enzyme jaundice (hyperbilirubinemia syndromes) or treatment with drugs that acidify the urine, such as ammonium chloride or ascorbic acid.

Elevated levels of urinobilinogen in the urine may indicate hemolytic anemia, a large hematoma, restricted liver function, liver infection, intoxication, or liver cirrhosis. that destroy the intestinal bacterial flora.

Low levels of urobilinogen in the urine can also be the result of congenital enzyme jaundice (hyperbilirubinemia syndromes) or treatment with drugs that acidify the urine, such as ammonium chloride or ascorbic acid.

Elevated levels of urinobilinogen in the urine may indicate hemolytic anemia, a large hematoma, restricted liver function, liver infection, intoxication, or liver cirrhosis.

Urobilinogen test

Urobilinogen test principle, evaluation, diagnosis:

This test is an indicator of liver disease. In combination with bilirubin, it helps to differentiate between the different forms of jaundice.

Principle : The test paper contains a stable diazonium salt that produces a reddish azo compound with urobilinogen.

Evaluation : depending on the color of the urine, 0.5 to 1 mg of urobilinogen / dI of urine is indicated. 1 mg / dl is considered the normal excretion rate. Higher values ​​are pathological. The strips cannot detect a complete absence of urobilinogen in the urine, which is also pathological. The colored fields correspond to the following urobilinogen concentrations:

  • Normal (0 – 1), 2, 4, 8,12 mg / dl o.
  • Normal (0 – 17), 34, 70,140, ​​200 μmol / l.

The test is inhibited by higher concentrations of formaldehyde. Prolonged exposure of urine to light leads to low or falsely negative results.

Higher or false positive results can be caused by the presence of diagnostic or therapeutic dyes in the urine. Greater amounts of bilirubin produce a yellow coloration.

Diagnosis : An increased urobilinogen concentration in the urine is a sensitive index of liver dysfunction or hemolytic diseases.

Urobilinogenuria is caused, for example, by viral hepatitis, chronic hepatitis, liver cirrhosis, infections, poisonings, congestion or carcinoma of the liver, hemolytic and pernicious anemine, polycythemia, and pathological state of the intestinal tract with increased resorbency.