Reference Intervals
| Canine | ≥ 10.9 µg/L |
|---|---|
| Feline | 12.0 – 82.0 µg/L |
Turnaround: 2-3 business days after receipt of samples.
Please note: Administration of oral pancreatic extracts does not affect serum TLI concentrations in either normal dogs/cats or those with EPI.
Sample
- 0.5 ml fasting (8-12 hours) non-hemolyzed serum for canines
- 0.2 ml fasting (8-12 hours) non-hemolyzed serum for felines
Interpretation
Canine trypsin-like immunoreactivity assay
Important: New reference interval and decision thresholds for cTLI assay (updated 3/24)
The cTLI assay we use is a commercial assay made by Siemens that is widely used by veterinary diagnostic laboratories world-wide. We recently became aware that there are dogs with a serum cTLI concentration that is higher than the cut-off value of ≤ 2.5 µg/L that appear to have exocrine pancreatic insufficiency (EPI). We gathered serum samples from more than 100 healthy dogs to determine if there had been an assay shift, which does appear to be the case. Thus, we have adjusted our reference interval to ≥ 10.9 to µg/L. Importantly, we needed to determine a cut-off value for the diagnosis of EPI in dogs. With help from many of our valued veterinarian clients, we recently completed an observational study to determine a new cut-off value for the shifted assay. We now consider values ≤ 5.5 µg/L to be diagnostic for EPI. Our recommendation for dogs with cTLI concentrations between 5.6 to 7.5 µg/L AND clinical signs consistent with EPI is to initiate a trial with pancreatic enzyme replacement therapy and to closely monitor the patient’s response. Please note that some dogs with small intestinal disease, but without EPI, can partially respond to pancreatic enzyme replacement therapy. Further, repeating a measurement of serum cTLI 1 to 2 months after initial blood sampling can be helpful to determine whether serum cTLI has further decreased and the dog has EPI. In such equivocal cases, samples should be collected after withholding food for 12 to 18 hours. Dogs with cTLI concentrations between 7.6 to 10.8 µg/L are unlikely to have EPI and other differential diagnoses should be considered depending on the clinical signs observed.
Also, some healthy dogs have serum cTLI concentrations >50 µg/L, but cTLI concentrations may also be increased in dogs with pancreatitis or renal insufficiency. Therefore, the clinical significance of a cTLI concentration >50.0 µg/L is uncertain. If you are concerned about pancreatitis, consider running a serum cPLI test as this test is more reliable for diagnosing this condition. In dogs without clinical signs of pancreatitis or with a serum cPLI concentration within the reference interval, a cTLI >50 µg/L is unlikely to be clinically important.
We will keep working to further refine these decision thresholds and as always, we are available to consult on challenging cases.
| 0 to 5.5 µg/L | Diagnostic for EPI |
| 5.6 to 7.5 µg/L | Subnormal cTLI concentration, EPI cannot be excluded. If signs are consistent with EPI, consider assessing response to pancreatic enzyme replacement therapy and/or remeasuring serum cTLI concentration in 1 to 2 months using a fasted sample (enzyme therapy will not interfere with testing). |
| 7.6 to 10.8 µg/L | Subnormal cTLI concentration, but EPI is unlikely. Consider other differential diagnoses depending on the clinical signs observed. |
| 10.9 to 50.0 µg/L | Result is within the reference interval. |
| > 50.0 µg/L | In dogs without clinical signs of pancreatitis or with normal cPLI concentrations, a cTLI > 50 µg/L is unlikely to be clinically important. |
Feline trypsin-like immunoreactivity assay
In cats, values equal to or below 8.0 µg/L are diagnostic for EPI, with values between 8.0 and 12.0 µg/L being equivocal. For equivocal results, repeating the assay one month later should be considered.
Serum fTLI values above 100.0 µg/L may be associated with either acute or chronic pancreatitis or decreased renal excretion due to severe renal insufficiency, although our experience suggests that serum TLI is often minimally increased even in severe renal failure. Elevated serum TLI concentrations are also seen without any apparent reason in or in some cats with intestinal disease without apparent pancreatitis.
Because increased serum TLI concentrations are not specific for pancreatitis it is important to perform a PLI test before concluding a patient has pancreatitis. Serum TLI is increased in only approximately 30 to 40% of cats (and dogs) with pancreatitis. Therefore, normal test results do not rule out the possibility of pancreatic inflammation. If pancreatitis is suspected, a PLI test should be performed.
| 0 to 8 µg/L | Diagnostic for exocrine pancreatic insufficiency (EPI). |
| 8.1 to 11.9 µg/L | Result is equivocal for exocrine pancreatic insufficiency. TLI should be repeated in 1-2 months. Ensure animal is fasted 8-12 hours before sample is taken. |
| 12.0 to 82.0 µg/L | Result is within the reference interval. |
| 82.1 to 99.9 µg/L | Mildly increased serum fTLI concentration. Consider measurement of serum fPLI concentration. |
| > 100.0 µg/L | Values of higher than 100 ug/L can be seen in cats with gastrointestinal disease, pancreatitis, and other conditions. A fPLI will allow for more specific assessment of your patient for pancreatitis. Also consider checking serum cobalamin and folate to assess small intestinal absorption. |
Stability
Serum TLI is extremely stable and serum can be shipped at ambient temperatures.
Please see other assays’ stability and shipping recommendations if requesting additional testing in addition to TLI.
Background Information
Exocrine pancreatic insufficiency (EPI) occurs as a consequence of insufficient synthesis and secretion of digestive enzymes by the pancreatic acinar tissue. The functional reserve of the pancreas is considerable, however, and EPI only develops when the exocrine secretory capacity is reduced to less than 10 – 15% of normal. At this point residual pancreatic function together with extra-pancreatic mechanisms of digestion cannot support adequate nutrient digestion and so weight loss, diarrhea, and other clinical signs ensue.
Assay Principle
Small quantities of zymogens (inactive precursor molecules) of pancreatic proteases are present in the blood of normal animals. Trypsinogen is synthesized exclusively by the acinar cells of the pancreas, and measurement of this zymogen by assay of TLI provides an excellent indirect index of pancreatic function. This assay detects both trypsinogen and trypsin (hence the use of the term TLI to describe the total concentration of these two immunoreactive species), but the active enzyme (trypsin) is only present in the serum when there is pancreatic inflammation.
Special Considerations
Administration of oral pancreatic extracts does not affect serum TLI concentrations in either normal dogs/cats or those with EPI. Therefore withdrawal of enzyme replacement therapy prior to testing of dogs/cats that are already receiving supplementation is unnecessary. Additionally, remeasuring serum TLI in patients with confirmed EPI is unwarranted.
Additionally, assays of serum cobalamin (vitamin B12) and folate are strongly recommended whenever serum TLI is assayed. Hypocobalaminemia is common in dogs and cats with EPI and cobalamin deficiency is the only independent risk factor for a poor treatment outcome in pets with EPI. Cobalamin supplementation may be essential before an optimal response to pancreatic enzyme replacement therapy is achieved.
Additional Reading
- Williams DA. The Pancreas. In: Strombeck DR, Guilford WG, Center SA, Williams DA, Meyer DJ, eds. Small Animal Gastroenterology. Philadelphia: W.B. Saunders 1996:381-410.
- Williams DA, Batt RM. Sensitivity and specificity of radioimmunoassay of serum trypsin-like immunoreactivity for the diagnosis of canine exocrine pancreatic insufficiency. J.Am.Vet.Med.Assoc. 1988;192:195-201.
- Steiner JM, Williams DA. Feline exocrine pancreatic disorders. The Veterinary Clinics of North America 1999;29:551-75.teiner JM, Williams DA, Moeller EM, Melgarejo TL. Development and validation of an enzyme-linked immuno sorbent assay (ELISA) for feline trypsin-like immunoreactivity (fTLI). Am.J.Vet.Res. 2000;61:620-3.
- Bruner JM, Steiner JM, Williams DA, Van Alstine WG, Blevins W. High feline trypsin-like immunoreactivity in a cat with pancreatitis and hepatic lipidosis. J Am.Vet.Med.Assoc. 1997;210:1757-60.
- Parent C, Washabau RJ, Williams DA et al. Serum trypsin-like immunoreactivity, amylase and lipase in the diagnosis of feline acute pancreatitis. J.Vet.Int.Med. 1995;9:194 (abstr).
- Swift NC, Marks SL, MacLachlan NJ, Norris CR. Evaluation of serum feline trypsin-like immunoreactivity for the diagnosis of pancreatitis in cats. Journal of American Veterinary Medical Association 2000;217:37-42.
- Steiner JM, Williams DA. Disagrees with criteria for diagnosing pancreatitis in cats. J.Am.Vet.Med.Assoc. 2000;217:816-7.
- Steiner JM, Williams DA. Serum feline trypsin-like immunoreactivity in cats with exocrine pancreatic insufficiency. J.Vet.Intern.Med. 2000;14:627-9.
