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175) An 8-year-old girl with cystic fibrosis (i.e., a positive sweat test and homozygous for the cystic fibrosis transmembrane regulator gene [CFTR] ΔF508 mutation) is transferring her care to a new pediatrician. The patient had a diagnosis of pancreatic insufficiency for which she has been treated with oral pancreatic enzyme replacement therapy. The physician wants to confirm the diagnosis of pancreatic insufficiency and collects a stool sample for fecal elastase testing. The stool is watery and poorly formed. Which one of the following reasons would cause the laboratory to reject this specimen?

Fecal elastase measurements should be performed only on adult patient samples because pediatric reference ranges do not exist. Fecal elastase measurements should not be performed on patients who are receiving pancreatic replacement therapy. Fecal elastase measurements should be performed only on well-formed stools. Fecal elastase measurement is not indicated for the diagnosis of pancreatic insufficiency. Fecal trypsin, not fecal elastase, measurement should be performed.

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• Fecal elastase is stable during transit through the bowel.

• Fecal elastase is concentrated in well-formed stools by fourfold to fivefold.

• The test is adequate for the diagnosis of severe pancreatic insufficiency but loses sensitivity in the setting of milder deficiencies.

• Fecal elastase is a better biomarker for pancreatic insufficiency than other pancreatic enzymes in stool.

• This biomarker is not affected by exogenous oral enzyme replacement.

Wiwanitkit V: Faecal elastase-1 (EL-1) in pediatric patients with cystic fibrosis. J Pediatr (Rio J) 2011;87(3):273.

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Clinical Pathology: Clinical Chemistry

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