The clinical and laboratory impact of reporting faecal elastase-1 in watery stool samples

Low faecal elastase-1 (FE-1) results are suggestive of pancreatic insufficiency, but watery diarrhoea may lead to falsely low results.

FE-1 results reported on watery samples over a three-year period were reviewed. Results in watery samples were compared to those from a formed sample. The follow-up of patients in whom an FE-1 result ≤199 ug/g stool (Schebo ELISA) was reported on a watery sample was also reviewed.

In total, 288 watery samples were identified. All results (19/19) ≥200 ug/g in watery samples were also ≥200 ug/g when measured in a formed sample from the same patient. There were 41 results ≤199 ug/g in watery samples, of which 29 (71%) were ≥200 ug/g when measured in a formed sample. Thirty-seven patients with a single FE-1 value ≤199 ug/g from a watery sample were followed up. Pancreatic Enzyme Replacement Therapy (PERT) was commenced in 15 patients. This was inappropriate in at least one patient. Reporting practice was subsequently changed to not report FE-1 values ≤199 ug/g in watery samples. This change was assessed after 12 months. Repeat samples were received from 15/56 (27%) of patients. Overall, 10/15 (67%) of samples were ≥200 ug/g on repeat. PERT was not commenced inappropriately in any of these patients.

There is value in measuring FE-1 in watery samples, as 144/288 (50%) of watery samples analysed were ≥200 ug/g, enabling a diagnosis of exocrine pancreatic insufficiency to be excluded. Not reporting FE-1 values ≤199 ug/g in a first-time watery stool samples appears clinically safe and has potentially reduced inappropriate diagnoses and prescribing.