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Test for exocrine pancreatic function (5mark)

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exocrine pancreatic insufficiency diagnostic tests fecal elastase secretin stimulation test guideline

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Tests of exocrine pancreatic function

They are classified as direct and indirect tests.
1. Direct pancreatic function tests
  • Secretin stimulation test: After IV secretin, duodenal aspirate is collected and volume, bicarbonate concentration, and enzyme output are measured. Reduced bicarbonate output indicates pancreatic insufficiency. It is sensitive but invasive.
  • Secretin-CCK (pancreozymin) test: Secretin assesses bicarbonate secretion; CCK assesses enzyme secretion (amylase, lipase, trypsin). This is a reference test for mild exocrine dysfunction.
2. Indirect tests
  • Fecal elastase-1: Most commonly used non-invasive screening test.
    • 200 micrograms/g stool: normal
    • 100-200 micrograms/g: indeterminate/mild insufficiency
    • <100 micrograms/g: severe pancreatic exocrine insufficiency
      A formed stool sample is needed because watery stool can give falsely low values.
  • 72-hour fecal fat estimation / coefficient of fat absorption: Demonstrates fat malabsorption (steatorrhea); considered a reference measure of fat maldigestion but is cumbersome.
  • 13C mixed-triglyceride breath test: Measures digestion and absorption of a labelled triglyceride; reduced expired 13CO2 suggests lipase deficiency.
  • Serum trypsinogen: Very low levels support severe pancreatic insufficiency, but it is insensitive in mild disease.
  • Older tests include fecal chymotrypsin and the Lundh meal test.
Key point: Fecal elastase-1 is the preferred first-line practical test, while secretin-based tests directly assess pancreatic secretion but are invasive. The UK practical guideline considers coefficient of fat absorption the reference diagnostic test for pancreatic exocrine insufficiency and recommends fecal elastase as the suitable first-line test.
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