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When a TLI test results comes back
between 2.6 and 5.6… explained!


         A cTLI test value less than 2.5ug/L is the current “gold standard” for a diagnosis of EPI. However, there is an “equivocal” range between 2.6 and 5.6 ug/L in which the ability of the test to confirm or rule out EPI is less certain. While dogs with cTLI values in this “equivocal” range do not meet the criteria for a diagnosis of EPI, some (especially at the low end of the range) may still benefit from pancreatic enzyme supplementation. There are at least three potential explanations for this observation. 

         First, it is possible for the cTLI value of a dog with EPI to be above the diagnostic cut-off value of 2.5 ug/L at any single sampling time based on natural fluctuations in the patient (if tested on repeated days the cTLI will not be exactly the same). Normally this makes no difference to interpretation of the result, since for example if a patient’s results vary between 1 and 2 ug/L they are still low and consistent with EPI. Similarly, normal results will always be normal. 

·         A second cause of variation is the inherent limits of precision of the cTLI test itself (or any similar laboratory test) – if you test the same sample repeatedly on the same day or different days you will not get exactly the same result. Again, this unavoidable variation usually is of no clinical significance – the results always indicate EPI (or normal). However, when the result is at the upper level of the diagnostically low range or the lower end of the equivocal range, there is inherent uncertainty. This means that a dog with a cTLI value of 3.2 may not be that different from one with a cTLI of 2.4 and may still have a severe enough deficiency in pancreatic enzyme production to warrant enzyme supplementation. Veterinarians often consult with us regarding management of these patients, and we make individualized recommendations based upon all the clinical information available.

         Third, it is also possible that some dogs with a cTLI at the lower end of the 2.6-5.6 ug/L range may respond to pancreatic enzyme supplementation due to individual variability in the production of digestive enzymes from other parts of the body. For example, normal dogs digest about 20% of the fat in their food using a gastric lipase made in the stomach. This is quite a different enzyme than the pancreatic lipase made by the pancreas, that digests most of the food in the diet, and that is deficient in dogs with EPI. However, some dogs produce far more gastric lipase, and some far less, than the average. If a dog with normally low production of lipase from the stomach develops a more mild degree of exocrine pancreatic damage than a typical dog with EPI, they may benefit from pancreatic enzyme supplementation because they are very dependent on pancreatic digestive enzymes and have much more limited ability to compensate with gastric lipase. 

         If your dog’s health has improved with the addition of pancreatic enzymes, it may be prudent to continue this therapy.

         If your dog has persistent clinical signs of gastrointestinal disease (weight loss, changes in appetite, vomiting, soft stool/diarrhea), despite enzyme supplementation, we recommend that you discuss other diagnostic and treatment options with your primary care veterinarian, as EPI may not be the primary, or only, cause of your pet’s illness.

         In the overwhelming majority of cases results of serum cTLI testing are absolutely clear-cut and interpretation is unequivocal. Very few tests in medicine give such “black and white” results. Nonetheless, after decades of experience interpreting serum cTLI test results, there are certainly rare individual patients whose cTLI values are unexpected and perhaps even seemingly inexplicable, especially on repeat testing. Simplified interpretation algorithms cannot cover all these eventualities, but after consultation with a specialist and discussions with the owner, veterinarians can usually come up with a logical plan to help manage the patient’s clinical problems most effectively.

Patrick Barko, DVM 

David Williams, MA VetMB PhD DACVIM ECVIM-CA