False Low Fecal Elastase-1 Results: Key Causes
The most common cause of a falsely low FE-1 result is watery or liquid stool, which dilutes the enzyme concentration and can produce false-positive results for pancreatic insufficiency. 1, 2
Primary Cause: Stool Consistency
- Watery or liquid stools are the leading cause of falsely low FE-1 values due to dilution of the enzyme concentration 1, 2
- In one study, 71% of FE-1 results ≤199 µg/g in watery samples normalized to ≥200 µg/g when measured in a formed sample from the same patient 2
- The test must be performed on semi-solid or solid stool specimens to ensure accurate results 1
- Diarrhea (defined as >85% stool water content) can result in falsely decreased elastase-1 levels in patients with non-pancreatic causes of diarrhea 3
Secondary Causes: Intestinal Pathology
Acute Enteritis and Infectious Diarrhea
- Transient small bowel damage from enteric pathogens (both bacterial and viral) can cause temporarily low FE-1 levels 4
- In children with acute enteritis, 12% showed severe FE-1 levels (<100 µg/g) and 16% showed moderate levels (100-200 µg/g), compared to 100% normal results in controls 4
- This transient pancreatic insufficiency is likely related to reduced enteric CCK secretion from intestinal damage 4
- Serial measurements in these patients show progressive normalization of FE-1 levels as the enteritis resolves 4
Inflammatory Bowel Disease
- Patients with inflammatory bowel disease may show abnormally low FE-1 values, particularly in the setting of severe protein malnutrition 5
- Patients with ileo-anal pouch anastomosis and pouchitis can have falsely low results, possibly due to bacterial elastase degradation 5
- FE-1 values may revert to normal after adequate treatment of the underlying IBD 5
Celiac Disease and Other Enteropathies
- Duodenal diseases including celiac disease and Crohn's disease can affect FE-1 results through alteration of enteric hormone release 1, 4
- Enteropathy may cause decreased exocrine pancreatic enzyme secretion through disruption of normal intestinal-pancreatic signaling 4
Clinical Implications and Pitfalls
Critical Testing Requirements
- Never interpret a low FE-1 result from a watery stool sample without repeat testing on a formed specimen 2
- Some laboratories have adopted policies to not report FE-1 values ≤199 µg/g in first-time watery stool samples, which has reduced inappropriate diagnoses and PERT prescribing 2
- When watery stools are unavoidable, lyophilization (freeze-drying) of stool samples can prevent false-low results by correcting for water content 3
Risk of Inappropriate Treatment
- Reporting low FE-1 values from watery samples led to inappropriate initiation of pancreatic enzyme replacement therapy (PERT) in at least some patients 2
- A therapeutic trial of pancreatic enzymes is unreliable for EPI diagnosis and should not be used to confirm a questionable FE-1 result 1
When to Suspect a False-Positive Result
- Any low FE-1 result in the setting of acute diarrhea or gastroenteritis should be repeated after resolution of symptoms 4
- Low FE-1 in patients with active IBD or pouchitis warrants repeat testing after treatment of the inflammatory condition 5
- Absence of high-risk conditions (chronic pancreatitis, pancreatic cancer, cystic fibrosis, prior pancreatic surgery) should raise suspicion for a false-positive result 1
Practical Algorithm for Interpreting Low FE-1
Step 1: Assess stool consistency at time of collection
- If watery/liquid → Do not interpret; request repeat sample when stool is formed 1, 2
- If semi-solid/solid → Proceed to Step 2
Step 2: Evaluate for acute intestinal illness
- If acute enteritis, gastroenteritis, or new-onset diarrhea → Defer testing until symptoms resolve 4
- If chronic stable symptoms → Proceed to Step 3
Step 3: Assess for inflammatory bowel conditions
- If active IBD, pouchitis, or untreated celiac disease → Treat underlying condition first, then retest 5
- If no active enteropathy → Proceed to Step 4
Step 4: Correlate with clinical risk factors