TLI (cTLI, fTLI) in cats and dogs

What it shows

Trypsinogen is made only by the acinar cells of the pancreas — the cells that produce digestive enzymes. A little normally leaks into the blood, and the test measures it together with trypsin: the fewer working acinar cells, the lower the TLI. The pancreas has a large reserve: EPI develops only when about 90% of the exocrine tissue is lost, so TLI answers the question “does the pancreas make enough enzymes?”.

The test is species-specific. cTLI is the canine test, fTLI a separate feline one; their results and cut-offs are not interchangeable between species.

TLI and PLI are easy to confuse. TLI (cTLI, fTLI) shows whether the pancreas makes too little enzyme — insufficiency. Pancreatic lipase immunoreactivity (PLI: cPL, fPL) shows whether the pancreas is inflamed — pancreatitis. TLI rises in only about 30–40% of cats and dogs with pancreatitis, so a normal TLI does not rule pancreatitis out, and a high TLI does not prove it.

Higher than reference — what it may be a sign of

• Pancreatitis — with inflammation active trypsin can appear in the blood, but the rise is inconsistent; when pancreatitis is suspected, the test to order is PLI.
• Kidney disease — can raise TLI, in cats often only slightly.
• Malnutrition — listed among the causes of high cTLI in dogs.
• Other gut disease — in cats a markedly high fTLI can occur with gastrointestinal disease, pancreatitis or other conditions.

A cTLI above 50 µg/L in a dog without signs of pancreatitis or with a normal cPL is unlikely to be clinically important.

Lower than reference

A low TLI is what the test is designed to find. The laboratory considers a value at or below its diagnostic cut-off diagnostic for EPI; the vet makes the decision. Values below the reference interval but above that cut-off are a grey zone where EPI is neither proven nor excluded. EPI can result from:

• Pancreatic acinar atrophy — the most common cause in German Shepherd Dogs.
• Chronic pancreatitis — the most common cause in dogs of other breeds and in cats.
• Masses that block the pancreatic duct — a rare cause.

Look at together with

• Cobalamin (B12) and folate — measuring them with TLI is strongly recommended: low B12 is common in EPI, and the bacterial overgrowth that often accompanies it can push folate up.
• Pancreatic lipase (cPL, fPL) — the test for pancreatitis. Chronic pancreatitis can end in EPI, so in some animals both questions come up.
• Lipase and amylase — general pancreatic enzymes; for EPI the test of choice is TLI, for pancreatitis — PLI.

Units and conversion

cTLI and fTLI are reported in µg/L; some labs write ng/mL, which is numerically the same — 1 ng/mL equals 1 µg/L. Nothing needs converting; canine and feline results are separate rows and are not compared with each other. In the app each row keeps the unit printed on the form.

Reference range

The reference range is on your lab’s form. For TLI the lower cut-off matters most. The figures below are the interpretation of the Texas A&M Gastrointestinal Laboratory; Merck gives the same diagnostic cut-offs. In dogs, cTLI at or below 5.5 µg/L is diagnostic for EPI; 5.6–7.5 µg/L is below the interval and EPI cannot be excluded, so the lab suggests measuring again on a fasted sample in 1–2 months; 7.6–10.8 µg/L is below the interval, but EPI is unlikely. The lab updated its canine interval in 2024 after a shift in the assay, so older forms may show other limits. In cats, fTLI at or below 8.0 µg/L is diagnostic for EPI, and above 8.0 up to 12.0 µg/L is equivocal, with a repeat 1–2 months later to consider.

Cats and dogs

Sources

1. Texas A&M Gastrointestinal Laboratory — Serum Trypsin-Like Immunoreactivity (TLI)
2. Exocrine Pancreatic Insufficiency in Dogs and Cats. Merck Veterinary Manual
3. Malabsorption Syndromes in Small Animals. Merck Veterinary Manual
4. VCA Animal Hospitals — Testing for Pancreatic Disease
5. VCA Animal Hospitals — Malabsorption and Bacterial Overgrowth in Dogs
6. Cornell University Animal Health Diagnostic Center — Canine, Feline and Equine Metabolic Function Tests