Which laboratory result is not characteristic of a complete obstruction of the common bile duct?

Which laboratory result is not characteristic of a complete obstruction of the common bile duct?

• A. Negative urine urobilinogen
• B. Negative fecal urobilinogen and urobilin
• C. Negative urine bilirubin
• D. Excretion of a pale-colored stool

Answer: (C)

Complete obstruction of the common bile duct causes bile to back up, leading to cholestasis. Because bile pigments can’t reach the gut, stool loses stercobilin and becomes pale. Meanwhile, conjugated bilirubin builds up in the blood and is excreted by the kidneys, so urine bilirubin is typically positive. The lack of bile entering the intestine also reduces the production of urobilinogen, so both urine urobilinogen and fecal urobilinogen/urobilin are negative or markedly reduced. The result that does not fit this pattern is negative urine bilirubin, since conjugated bilirubin is usually present in the urine with complete CBD obstruction.

Complete obstruction of the common bile duct causes bile to back up, leading to cholestasis. Because bile pigments can’t reach the gut, stool loses stercobilin and becomes pale. Meanwhile, conjugated bilirubin builds up in the blood and is excreted by the kidneys, so urine bilirubin is typically positive. The lack of bile entering the intestine also reduces the production of urobilinogen, so both urine urobilinogen and fecal urobilinogen/urobilin are negative or markedly reduced. The result that does not fit this pattern is negative urine bilirubin, since conjugated bilirubin is usually present in the urine with complete CBD obstruction.