What specimen should be collected for pancreatic elastase testing?

Specimen Collection for Pancreatic Elastase Testing

Pancreatic elastase testing must be performed on a semi-solid stool specimen. 1

Proper Specimen Collection and Handling

• A single stool sample of approximately 100 mg is required for fecal elastase-1 (FE-1) testing 2
• The stool must be semi-solid in consistency, not liquid 1, 2
• The specimen remains stable for up to one week at room temperature, making collection and transport convenient 2
• Testing can be performed while the patient is on pancreatic enzyme replacement therapy (PERT) as this does not affect the results 2, 3

Important Considerations for Accurate Results

Potential for False Results

• Liquid stool samples can lead to falsely low elastase levels due to dilution effects 2
• Significant variation can occur within a single stool passage (mean coefficient of variation = 22%) 4
• Day-to-day variation in fecal elastase levels can be considerable (mean coefficient of variation = 26%) 4

Recommendations to Improve Accuracy

• Collect multiple stool samples on different days to account for variation 4
• Ensure proper consistency of stool (semi-solid) to avoid false-negative results 1, 2
• Be aware of the borderline area of ±25% around the cutoff value of 200 μg/g when interpreting results 4

Interpretation of Results

Fecal elastase levels are interpreted as follows:

• 200 μg/g: Normal pancreatic function

• 100-200 μg/g: Indeterminate for exocrine pancreatic insufficiency (EPI)
• <100 μg/g: Good evidence of EPI
• <50 μg/g: Severe EPI 2

Clinical Context

• Fecal elastase testing is the most appropriate initial test for suspected EPI 1
• The test has high sensitivity (100%) for moderate to severe chronic pancreatitis but lower sensitivity for mild cases 3, 5
• Specificity is approximately 83%, making it more reliable than some other indirect pancreatic function tests 3
• This non-invasive test has largely replaced more invasive testing methods for pancreatic function 2

Pitfalls to Avoid

• Do not collect liquid stool samples as they can lead to falsely low results 2
• A single sample may not be representative due to significant intra-individual variation 4
• Be cautious when interpreting borderline results (100-200 μg/g) as they are indeterminate for EPI 1, 2
• The test has limited utility in detecting mild pancreatic insufficiency (sensitivity <60%) 2

Following these guidelines for proper specimen collection will help ensure accurate diagnosis of exocrine pancreatic insufficiency, allowing for appropriate treatment decisions that can significantly impact patient morbidity, mortality, and quality of life.