Trypsin-Like Immunoreactivity

By Krista Williams, BSc, DVM, CCRP; Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc

What is trypsin-like immunoreactivity?

Trypsinogen is a proenzyme (a non-activated enzyme) that is secreted into the small intestine by the pancreas, along with other pancreatic digestive enzymes. When it reaches the small intestine, trypsinogen is converted to trypsin, an enzyme that helps to digest proteins. In healthy animals, a small amount of trypsinogen escapes from the pancreas into the blood circulation and can be measured in a blood sample by a test called trypsin-like immunoreactivity.

How is the measurement of trypsin-like immunoreactivity (TLI) used?

TLI measurement is primarily used for the diagnosis of exocrine pancreatic insufficiency. This disease involves the portion of the pancreas that produces digestive enzymes. Insufficient enzyme production results in improper digestion of fats, carbohydrates, and proteins. The clinical signs shown by the patient include the production of large volumes of fatty feces and weight loss.

Dogs with exocrine pancreatic insufficiency have reduced functional pancreatic tissue and so less trypsinogen is produced. Therefore, less trypsinogen escapes into the blood circulation, resulting in low levels of serum TLI.

How is trypsin-like immunoreactivity measured?

A single fasting blood sample is sent to a veterinary referral laboratory for trypsin-like immunoreactivity determination.

Do all dogs with exocrine pancreatic insufficiency have decreased trypsin-like immunoreactivity blood values?

Typically, by the time that clinical signs of exocrine pancreatic insufficiency are apparent most dogs will have significantly reduced concentrations of trypsin-like immunoreactivity.

However, if a dog has concurrent pancreatitis, or if a sample is taken shortly after a meal, the amount of trypsin-like immunoreactivity may be temporarily increased into the normal range.

Are there any other uses for trypsin-like immunoreactivity?

Trypsin-like immunoreactivity has been used occasionally in the diagnosis of pancreatitis (inflammation of the pancreas). However, this test does not reliably diagnose pancreatitis.

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