Urine Bilirubin

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The fixed phagocytic cells of the spleen and bone marrow destroy old red blood cells and convert the heme groups of hemoglobin to the pigment bilirubin. The bilirubin is secreted into the blood and carried to the liver where it is bonded to (conjugated with) glucuronic acid, a derivative of glucose. Some of the conjugated bilirubin is secreted into the blood and the rest is excreted in the bile as bile pigment that passes into the small intestine. The blood normally contains a small amount of free and conjugated bilirubin.

Bilirubin is a normal byproduct of the body. As red blood cells, the cells that carry oxygen to the body, wear out, they are filtered out through the liver. The liver, when functioning correctly, will send these useless blood cells (bilirubin) out of the body by means of the large intestine. Normally, your kidneys, which produce urine, will not have to filter out the dead red blood cells. However, when the liver isn't functioning properly, bilirubin is filtered by the kidneys and comes out in the urine instead of through your colon.

Normally, a tiny amount of bilirubin is excreted in the urine if any. If the liver's function is impaired or when biliary drainage is blocked, some of the conjugated bilirubin leaks out of the hepatocytes and appears in the urine, turning it dark amber. The presence of this conjugated bilirubin in the urine can be clinically analyzed, and is reported as an increase in urine bilirubin. However, in diseases involving hemolytic anemia, an increased number of red blood cells are broken down, causing an increase in the amount of unconjugated bilirubin in the blood. As stated above, the unconjugated bilirubin is not water soluble, and thus one will not see an increase in bilirubin in the urine. Because there is no problem with the liver or bile systems, this excess unconjugated bilirubin will go through all of the normal processing mechanisms that occur (e.g., conjugation, excretion in bile, metabolism to urobilinogen, reabsorption) and will show up as an increase in urine urobilinogen. This difference between increased urine bilirubin and increased urine urobilinogen helps to distinguish between various diseases in those systems.

Test results
An abnormally high level of bilirubin may result from: an increased rate of red blood cell destruction, liver damage, as in hepatitis and cirrhosis, and obstruction of the common bile duct as with gallstones. An increase bilirubin results in jaundice, a condition characterized by a brownish yellow pigmentation of the skin and of the sclera of the eye.
Abnormal bilirubin values may indicative of:
·Pre-hepatic (unconjugated bilirubin therefore does not appear in urine)  
·excessive breakdown of RBC  
·obstruction of biliary duct  
·toxic liver damage  
·biliary tree obstruction  

Also you should know
Whether the cause is liver disorder, hepatitis, or a blocked common bile duct, only a blood test and ultrasound of your liver and liver enzymes will determine the cause of the jaundice and urinary bilirubin. The doctor will order an AST and ALT count. These are liver enzymes. If they are above or below the normal levels, hepatitis will be suspected. The doctor will also order an ultrasound of your liver to see if it is inflamed. After all of these tests have been performed, an accurate diagnosis can be made.

Jaundice may be noticeable in the sclera (white) of the eyes at levels of about 2 to 3 mg/dL (34 to 51 mmol/L), and in the skin at higher levels. Jaundice is classified depending upon whether the bilirubin is free or conjugated to glucuronic acid into Conjugated jaundice or Unconjugated jaundice.

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