Which finding is not characteristic of cystic fibrosis?

Which finding is not characteristic of cystic fibrosis?

• A. Decreased bicarbonate concentration in duodenal fluid
• B. Decreased lipase activity in duodenal fluid
• C. Decreased amylase activity in duodenal fluid
• D. Increased trypsin in feces

Answer: (D)

Blockage of pancreatic ducts by thick secretions in cystic fibrosis reduces the flow of bicarbonate and digestive enzymes into the duodenum. That downstream effect shows up as decreased bicarbonate concentration in duodenal fluid and lowered activities of pancreatic enzymes like lipase and amylase in the duodenum, reflecting pancreatic exocrine insufficiency. Because the pancreas isn’t delivering enough enzymes to the gut, the stool typically has reduced levels of pancreatic enzymes and fat malabsorption, leading to steatorrhea. Increased trypsin in feces would not fit this pattern; trypsin activity in stool would be decreased, not elevated, in cystic fibrosis. (Meanwhile, elevated immunoreactive trypsinogen in blood is a newborn screening finding for CF, but that reflects circulating trypsinogen, not fecal trypsin.)

Blockage of pancreatic ducts by thick secretions in cystic fibrosis reduces the flow of bicarbonate and digestive enzymes into the duodenum. That downstream effect shows up as decreased bicarbonate concentration in duodenal fluid and lowered activities of pancreatic enzymes like lipase and amylase in the duodenum, reflecting pancreatic exocrine insufficiency.

Because the pancreas isn’t delivering enough enzymes to the gut, the stool typically has reduced levels of pancreatic enzymes and fat malabsorption, leading to steatorrhea. Increased trypsin in feces would not fit this pattern; trypsin activity in stool would be decreased, not elevated, in cystic fibrosis.

(Meanwhile, elevated immunoreactive trypsinogen in blood is a newborn screening finding for CF, but that reflects circulating trypsinogen, not fecal trypsin.)