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TLI-universal testing

The TLI Test – Used to test for EPI
TLI in Brief
updated September 5, 2023
  • To confirm EPI, schedule a TLI Blood Test
    (Updated website link)   
    (Previous website link)
  • Current fasting protocol (food only) for the patient 8-12 hours prior to blood draw (previous fasting protocol was12-15 hours)
  • Do test on Mon, Tue or Wed ONLY, especially when also doing recommended B12 assay at the same time.
  • As of Sept 2023 normal range is now under review and the new values that should be considered are as follows for dogs:
  • New cTLI interpretations:   DOGS

    0 to 2.5 µg/L Diagnostic for EPI
    2.6 to 7.5 µg/L Subnormal cTLI concentration, highly suggestive of EPI. Assess response to pancreatic enzyme replacement therapy to confirm diagnosis.
    7.6 to 10.0 µg/L Subnormal cTLI concentration, EPI cannot be excluded. If signs are consistent with EPI, consider assessing response to pancreatic enzyme replacement therapy to confirm diagnosis.
    10.1 to 50.0 µg/L Result is within the reference interval.
    >50.0 µg/L The clinical significance of a cTLI concentration >50.0 µg/L is uncertain. If you have also run a cPLI and this is within the reference interval pancreatitis is unlikely.

New fTLI interpretations:   CATS

0 to 8 µg/L Diagnostic for exocrine pancreatic insufficiency (EPI).
8.1 to 12 µg/L Result is equivocal for exocrine pancreatic insufficiency.  TLI should be repeated in 1-2 months.  Ensure animal is fasted 12-18 hours before sample is taken.
12.1 to 81.9 µg/L Result is within the reference interval.
82 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.
The TLI Test 

The gold-standard test to  confirm EPI is with a TLI (Trypsin-Like Immunoreactivity) blood test. If your dog is a newly diagnosed puppy with EPI, although not necessary, but if possible, talk to your vet about re-testing in a few months with another TLI test to eliminate any rare false-positive reads and confirm EPI. The only reason why this is mentioned here is because although almost all dogs that test positive for EPI do indeed have EPI- – there have been extremely rare cases of a false read. Out of over 1,000 dogs…I know of only two that this happened with.

The following is from Texas A&M University (TAMU) GI Laboratory explaining the TLI test:   Serum Trypsin-Like Immunoreactivity  (TLI)

Control Ranges: (normal ranges) REVISED September 5, 2023

Canine 10.1 – >50 µg/L
Feline 12.0 – 82.0 µg/L

*** To see assay schedule, testing and shipping instructions please directly visit TAMU’s GI website as noted above***

INTERPRETATION: revised September 5, 2023

Canine trypsin-like immunoreactivity assay

IMPORTANT: new reference interval and decision thresholds 

The cTLI assay we use is a commercial assay made by Siemens that is widely used by veterinary laboratories world-wide. We recently became aware that there are dogs with a cTLI that is higher than the current 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 whether maybe there has been an assay shift, which there does appear to be. Thus, we have adjusted our reference interval to 10.1 to >50.0 µg/L. Of course the more important question is what the cut-off value for diagnosing EPI in dogs should be. We have started a prospective observational study to determine the best cut-off value for the shifted assay. Until this study is completed, we have instituted provisional diagnostic thresholds and recommendations (see below). Values ≤2.5 µg/L are still considered to be diagnostic for EPI. Our recommendation for dogs with equivocal cTLI concentrations in the lower range (2.6 to 7.5 µg/L) is to initiate a trial with pancreatic enzyme replacement therapy and to closely monitor their response. Based on epidemiological data from more than 500,000 dogs we feel confident that these dogs likely have EPI. For dogs with equivocal cTLI concentrations in the higher range (7.6 to 10.0 µg/L), incorporate how well the dog’s clinical signs fit with EPI, whether other causes of these signs have been eliminated, and possibly the patient’s response to pancreatic enzyme replacement therapy.

Additionally, some healthy dogs have 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 cPLI test as this is more reliable for diagnosing this condition. In dogs without clinical signs of pancreatitis or with normal cPLI concentrations, a cTLI >50 µg/L is unlikely to be clinically important.

We will update you as soon as we have gathered enough prospective data to make more definitive recommendations. As always, we are available to consult on complex cases.


  • 0.5 ml fasting (8-12 hours) non-hemolyzed serum for canines
  • 0.2 ml fasting (8-12 hours) non-hemolyzed serum for felines



0.5 ml fasting (12-18 hours) non-hemolyzed serum for canines
0.2 ml fasting (12-18 hours) non-hemolyzed serum for felines  


Serum TLI is extremely stable and serum can be shipped at ambient temperatures. 


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. 


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 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.


Administration of oral pancreatic extracts does not affect serum TLI concentrations in either normal dogs or cats with EPI, so withdrawal of enzyme supplementation prior to testing of dogs and cats that are already receiving supplementation is unnecessary.

Additionally, assays of serum cobalamin (vitamin B12) is strongly recommended whenever serum TLI is assayed. Serum vitamin abnormalities are common in dogs and especially cats with EPI. Therapeutic supplementation may be essential before an optimal response to enzyme supplementation is obtained. 

EXPLANATION FOR POSSIBLE TLI VARIANCE:  Dr. David A. Williams, developer of the TLI test, said was that there are no absolutes. There is inherent variability in the TLI assay (as with any assay) and this variability is not the same across all values ? indeed the variation in the numerical value is greatest for low (especially within the ?EPI range?) and high values. So do not over-interpret the absolute values in the ?EPI range?. Anything that is reported as less than 2.0 should just be regarded as essentially undetectable. A dog with a reported value of 0.6 is no sicker than one with a value of 1.6, and by the same token, there is no reason to believe that it will need more enzymes or do less well. 

Regarding the variability in reported values, the way Dr. Williams explained it to me was that if you took one vial of blood and tested it (for example) on Tuesday at 1:00 and got one numeric value of 1.5? you can take more blood from that same vial and test it on the same equipment on the same Tuesday at 2:00 and get a different numeric value of maybe 1.0. Indeed, if you tested the same sample twice at the same time you still might get the same difference of 0.5 between the two sets of results! The more you did this; took an average of all the values you got from that one vial of blood tested on the same day on the same equipment would yield a more accurate value, but it still would not be all absolute. This is why, he explained, there is variability that does not reflect any significant difference, and both values are diagnostically low and indicative of EPI. Differences between test results of approximately 2.0 and approximately 3.0 are generally reproducible however, and of diagnostic and functional significance. While both are abnormally low values, the former is almost always associated with clinical signs while the latter almost never is. Fortunately, the vast majority of test results are usually clearly diagnostically low (less than 2.5) or clearly normal (greater than 5.0) so these niceties regarding the assay are of no practical consequence.  I hope this helps clarify why TLI values may somewhat fluctuate within the EPI range.  


  1. 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.
  2. 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.
  3. Steiner JM, Williams DA. Feline exocrine pancreatic disorders. The Veterinary Clinics of North America 1999;29:551-75.
  4. Steiner 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.
  5. 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.
  6. 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).
  7. 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.
  8. Steiner JM, Williams DA. Disagrees with criteria for diagnosing pancreatitis in cats. J.Am.Vet.Med.Assoc. 2000;217:816-7.
  9. Steiner JM, Williams DA. Serum feline trypsin-like immunoreactivity in cats with exocrine pancreatic insufficiency. J.Vet.Intern.Med. 2000;14:627-9.