Diagnosis of exocrine pancreatic insufficiency in dogs requires use of a newly adjusted reference range and diagnostic cutoff for measurement of trypsin-like immunoreactivity

Objective: To adjust the reference interval (RI) for a commercially available canine trypsin-like immunoreactivity (cTLI) assay and the cutoff value for the diagnosis of exocrine pancreatic insufficiency (EPI). Methods: Lower limit of the RI was calculated based on the fifth percentile of cTLI concentrations in 102 clinically healthy dogs. Questionnaires were sent to clinicians for cases with serum cTLI concentrations ≤ 10 µg/L. Five board-certified small animal internists blinded to serum cTLI concentration individually reviewed questionnaire responses to clinically classify each dog. Dogs were classified as "EPI" or "not EPI" based on the consensus when ≥ 4 internists assigned the same classification. The cutoff was determined by maximizing the weighted Youden index (1.34 × sensitivity + 0.67 × specificity - 1). Sensitivity was prioritized, as false negatives were considered more deleterious than false positives. Results: The calculated lower RI limit was ≥ 11.8 µg/L. Forty-seven dogs each were classified as EPI and not EPI. The median (range) serum cTLI concentrations were 1.5 µg/L (0.9 to 7.2) for the EPI dogs and 8.3 µg/L (2.2 to 10.0) for the not EPI dogs. The optimal diagnostic cutoff was 5.5 µg/L, with a sensitivity of 95.7% and specificity of 83.0%. Conclusions: Use of the updated RI (≥ 11.8 µg/L) and diagnostic cutoff value for EPI (5.5 µg/L) should reduce false-negative results when using this commercial assay. Clinical Relevance: There has been an upward shift in serum cTLI measurements with this commercial assay, consistent with clinical observations.