Urobilinogen is a compound derived from bilirubin, which is created when the body breaks down old red blood cells. It is a standard component of a urinalysis that measures substances in a urine sample. A small quantity of urobilinogen is normally found in urine, and its level serves as a health marker.
The Origin of Urobilinogen
Urobilinogen’s formation starts with the life cycle of red blood cells. These cells are broken down, primarily in the spleen, releasing hemoglobin. The hemoglobin is then processed, and its heme component is converted into a yellow pigment called bilirubin.
The liver takes up this bilirubin from the blood. Once in the liver, bilirubin is incorporated into a digestive fluid called bile. The liver then releases bile through small tubes, known as bile ducts, which lead into the small intestine to help digest fats.
Inside the intestines, gut bacteria metabolize the bilirubin in bile, converting it into urobilinogen. Most of this is then converted to stercobilin, the compound giving feces its brown color, and is excreted in stool.
A small portion of urobilinogen is reabsorbed from the intestines back into the bloodstream. It then travels to the kidneys, which filter it out of the blood and into the urine. This filtering process is why a small amount of urobilinogen is normal in a urine sample.
Interpreting High Urobilinogen Levels
Elevated urobilinogen in urine can be an early indicator of certain health issues, sometimes before other symptoms appear. A concentration greater than 2.0 mg/dL is considered abnormal. The two primary reasons for this increase are an overproduction of bilirubin or the liver’s inability to process reabsorbed urobilinogen.
One cause of high urobilinogen is the excessive breakdown of red blood cells, a condition known as hemolytic anemia. When red blood cells are destroyed too quickly, it results in a surge of bilirubin production. This overwhelms the liver, leading to more bilirubin in the intestines and a higher production of urobilinogen.
Another cause involves liver health, as conditions like hepatitis or cirrhosis damage liver cells. A damaged liver cannot efficiently filter the urobilinogen reabsorbed from the bloodstream. As a result, urobilinogen accumulates in the blood, leading to higher amounts being excreted by the kidneys into the urine.
Interpreting Low or Absent Urobilinogen
Very low or absent urobilinogen in a urine sample is also a significant medical finding. This result suggests that bilirubin is not reaching the intestines, preventing gut bacteria from producing urobilinogen. This leads to its absence in the bloodstream and urine.
A primary cause for this is a blockage in the bile ducts, which can be obstructed by gallstones or a tumor. This obstruction prevents the flow of bile from the liver and gallbladder into the intestine. The condition is often accompanied by pale or clay-colored stools because bile pigments are not reaching the gut.
Another reason for low urobilinogen can be a disruption to the gut microbiome. Broad-spectrum antibiotics can eliminate the intestinal bacteria responsible for converting bilirubin into urobilinogen. If these bacteria are absent, the conversion cannot happen, leading to a temporary decrease or absence of urobilinogen in the urine.
The Connection to Bilirubin in Urine
Distinguishing between urobilinogen and bilirubin on a urinalysis report is necessary for proper interpretation. While a small amount of urobilinogen in urine is normal, any bilirubin in urine, a condition called bilirubinuria, is abnormal. The two substances provide different but related information.
Bilirubin in the urine indicates that conjugated bilirubin, a water-soluble form processed by the liver, is entering the bloodstream and being filtered by the kidneys. This leakage from the liver into the blood suggests liver disease or a bile duct obstruction. It means the liver is processing bilirubin but cannot properly excrete it into the bile.
Test results for urobilinogen and bilirubin are interpreted together. For example, a bile duct obstruction might show low or absent urobilinogen but high levels of bilirubin in the urine. This pattern helps medical professionals differentiate between various liver and biliary system problems.