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Bilirubin is not normally detectable in the urine of healthy people. If the blood level of conjugated bilirubin becomes elevated, e.g. due to liver disease, excess conjugated bilirubin is excreted in the urine, indicating a pathological process. [60] Unconjugated bilirubin is not water-soluble and so is not excreted in the urine.
The former, referring to elevated unconjugated bilirubin, is often caused by haemolytic diseases resulting in increased bilirubin production and impaired bilirubin conjugation. The latter is often attributed to direct hepatocyte injury that impedes conjugated bilirubin secretion. [6]
The bilirubin present in the plasma is largely unconjugated in this setting as they haven't been taken up and conjugated by the liver. [3] In this case, total serum bilirubin increases while the ratio of direct bilirubin to indirect bilirubin remains 96 to 4 as up to 96%-99% of bilirubin in the bile are conjugated mentioned above. [9] [1]
Bilirubin is conjugated with glucuronic acid in the liver by the enzyme glucuronyltransferase, making it soluble in water. Much of it goes into the bile and thus out into the small intestine. Although 20% of the secreted bilirubinoid bile is reabsorbed by the small intestine, [2] conjugated
Urine: conjugated bilirubin present, urobilinogen > 2 units but variable (except in children) Plasma proteins show characteristic changes. Plasma albumin level is low, but plasma globulins are raised due to an increased formation of antibodies. Unconjugated bilirubin is hydrophobic, so cannot be excreted in urine.
Rotor syndrome (also known as Rotor type hyperbilirubinemia) [2] is a rare cause of mixed direct (conjugated) and indirect (unconjugated) hyperbilirubinemia, relatively benign, autosomal recessive [3] bilirubin disorder characterized by non-hemolytic jaundice due to the chronic elevation of predominantly conjugated bilirubin. [2]
Dubin-Johnson syndrome is caused by mutations in ABCC2/MRP2 which usually transports conjugated bilirubin out of the liver cell. Rotor syndrome is clinically similar to Dubin-Johnson syndrome but can cause a mixed hyperbilirubinemia, elevating both unconjugated and conjugated bilirubin levels in the blood.
It happens if conjugated bilirubin is present. In an indirect positive test, the patient's serum is first treated with alcohol and later mixed with diazo reagent. This causes development of a red colour. It is seen if unconjugated bilirubin is present. If both conjugated and unconjugated bilirubin are present the reaction is termed a biphasic ...