Urinalysis - The Carter Center

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4.4 Determination of Bilirubin
Introduction
Bilirubin is a waste product that must be eliminated from the body. It is
formed by the breakdown of hemoglobin in the reticuloendothelial cells
of the spleen and bone marrow, and then transported to the liver.
On its way to the liver it is not water-soluble, and is carried through the
blood stream linked to plasma albumin. This water insoluble form of
bilirubin is often referred to as free bilirubin or unconjugated bilirubin or
indirect bilirubin. Since this albumin - bound form is insoluble in water; it
does not appear in the urine. In the liver bilirubin is converted to a watersoluble
product by conjugation with glucuronic acid to form bilirubin
glucuronide. The water-soluble form is called cunjugated bilirubin. It is
also called direct bilirubin. The liver cells that form the conjugated
bilirubin excrete it into the bile and it is then excreted into the intestinal
tract through the bile duct. In the small intestine this conjugated
bilirubin is converted by intestinal bacteria to urobilinogen or
stercobilinogen.
Even though normally the level of conjugated bilirubin in the blood is not
high enough to cause significant amounts to appear in the urine, this
water soluble and conjugated bilirubin can be excreted by the kidneys.
Normal Value: approximately up to 0.02 mg/dl (This amount is not
detected by routine qualitative or semi quantitative techniques).
Clinical Significance
Tests for urinary bilirubin and urobilingen were normally performed only
indicated by abnormal color of the urine or when liver disease or a
hemolytic condition was suspected from the patient's history. The
presence of bilirubin and urobilinogen in the urine is an early sign of liver