In a patient of jaundice, absence of urobilinogen in urine indicates?
Correct Answer: Obstructive jaundice
Description: Ans. a. Obstructive jaundice (Ref: Harrison 19/e p280, 18/e p325)Absence of urinary urobilinogen is usually suggestive of obstructive jaundice."The conjugated bilirubin excreted into bile drains into the duodenum and passes unchanged through the proximal small bowel. Conjugated bilirubin is not taken up by the intestinal mucosa. When the conjugated bilirubin reaches the distal ileum and colon, it is hydrolyzed to unconjugated bilirubin by bacterial b-glucuronidases. The unconjugated bilirubin is reduced by normal gut bacteria to form a group of colorless tetrapyrroles called urobilinogens. About 80- 90% of these products are excreted in feces, either unchanged or oxidized to orange derivatives called urobilins. The remaining 10-20% of the urobilinogens are passively absorbed, enter the portal venous blood, and are re-excreted by the liver. A small fraction (usually <3 mg/dL) escapes hepatic uptake, filters across the renal glomerulus, and is excreted in urine. "-- Harrison 19/e p280Function testPrehepatic jaundiceHepatic jaundicePost-hepatic (Obstructive) jaundiceTotal bilirubinNormal/ increasedIncreasedQIncreasedQConjugated bilirubinNormalIncreasedQIncreasedQUnconjugated bilirubinNormal/ increasedIncreasedQNormalUrobilinogenNormal/ increasedDecreasedQDecreased/ negativeQUrine colorNormalDark (urobilinogen + conjugated bilirubin)QDark (conjugated bilirubin)QStool colorNormalNormal/paleQPaleQAlkaline phosphatase levelsNormalIncreasedQIncreasedQAlanine transferase & aspartate transferase levelsNormalincreasedQIncreasedQConjugated bilirubin in urineAbsentQPresentQPresentQSplenomegalyPresentQPresentQAbsentQ Bilirubin metabolism and eliminationNormal bilirubin production from heme (0.2-0.3 gm/day) is derived primarily from the breakdown of senescent circulating erythrocytes.Extrahepatic bilirubin is bound to serum albumin and delivered to the liver.Hepatocellular uptakeGlucuronidation in the endoplasmic reticulum generate bilirubin monoglucuronides & diglucuronides. which are water soluble and readily excreted into bile.Gut bacteria deconjugate the bilirubin and degrade it to colorless urobilinogens. The urobilinogens and the residue of intact pigments are excreted in the feces, with some reabsorption and excretion into urine.
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