Trypsin-Like Immunoreactivity

What is trypsin-like immunoreactivity (TLI)?

Trypsinogen is a proenzyme (a non-activated enzyme) that the pancreas secretes into the small intestine, along with other pancreatic digestive enzymes. When trypsinogen reaches the small intestine, it is converted to trypsin, an enzyme that helps 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 (TLI).

How is a TLI measurement 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. Clinical signs include weight loss and the production of large volumes of fatty feces.

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 TLI 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 TLI blood values?

Typically, by the time clinical signs of exocrine pancreatic insufficiency are apparent, most dogs have significantly reduced concentrations of TLI. However, if a dog has concurrent pancreatitis, or if a sample is taken shortly after a meal, TLI may be temporarily increased into the normal range.

Are there any other uses for TLI?

TLI is occasionally used in the diagnosis of pancreatitis (inflammation of the pancreas); however, it does not reliably diagnose pancreatitis. Newer tests, such as canine pancreatic lipase immunoreactivity (cPLI) are more reliable for diagnosing this condition.