Serum Trypsin-Like Immunoreactivity (TLI)
||5.7 - 45.2 µg/L
||12.0 - 82.0 µg/L
Turnaround: 1-2 business days after receipt of
In dogs, values below 2.5 µg/L are diagnostic for
EPI. Values between 3.5 and 5.7 µg/L are rarely if ever associated
with signs of EPI but may reflect subclinical pancreatic disease
such as subtotal pancreatic acinar cell destruction secondary to
on-going immune-mediated lymphocytic pancreatitis. Progression of
the disease in such patients may ultimately lead to EPI. Values
between 2.5 and 3.5 µg/L are sometimes (but rarely) associated with
clinical signs due to EPI. In these cases the TLI assay should be
repeated after one month paying particular attention to ensuring
that food is withheld for 12 to 15 hours before the blood sample is
In cats, values equal to or below 8.0 µg/L are
diagnostic for EPI, with values between 8.0 and 12.0 being
equivocal. As in the dog, repeating the assay one month later
should be considered.
Serum TLI values above 50.0 µg/L (dogs) and 100.0 µg/L (cats)
are consistent 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 in some malnourished patients (dogs
usually) without evidence of pancreatitis, and in some cats with
patchy pancreatic hypertrophy/atrophy (generally considered to be a
benign age-related change). Serum TLI is increased in approximately
30-40% of cats and dogs with pancreatitis; it is important to
recognize that normal test results do not rule out the possibility
of pancreatic inflammation. We believe that in acute pancreatitis
testing of samples obtained as soon as possible after the onset of
clinical signs is most likely to yield an abnormal test result. If
pancreatitis is suspected, a PLI
test should be performed. In cats increased serum TLI
is often also observed with small intestinal disease. In these
cases serum concentrations of cobalamin and folate
should be determined for evaluation of the small intestine.
- 0.5 ml fasting (12-18 hours) non-hemolyzed serum for
- 0.2 ml fasting (12-18 hours) non-hemolyzed serum for
Serum TLI is extremely stable and serum can be shipped at
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
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.
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) and folate
are 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.
- 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.
- Steiner JM, Williams DA. Feline exocrine pancreatic disorders.
The Veterinary Clinics of North America 1999;29:551-75.
- 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.
- 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.
- 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
- 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.
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