Cat & Dog - TLI Tests (Trypsin Like Immunoreactivity)

What is trypsin like immunoreactivity (TLI)?

Trypsin is an enzyme that is involved in the digestion of proteins in the small intestine.  It is secreted by the pancreas as trypsinogen which is a non-activated enzyme (pro-enzyme).  It becomes activated to trypsin once it is in the small intestine and then becomes involved in the digestion of proteins.

In normal, healthy animals, a small amount of trypsinogen enters the blood stream and this can be measured by the TLI test.

What is the importance of this test?

TLI determination is primarily used as a means of diagnosis of exocrine pancreatic insufficiency, (EPI).  EPI is a disease of the exocrine portion of the pancreas (the portion that is involved in the production of digestive enzymes).  Insufficient enzyme production results in improper digestion of fats, carbohydrates and proteins.  It is completely separate from the endocrine portion which is responsible for the production of insulin and other hormones which control glucose levels in the body.  Thus EPI is not involved with diabetes although with certain pancreatic gland problems both EPI and diabetes do occur.

EPI is common in German Shepherd Dogs and some other breeds.   The clinical signs include diarrhoea, large quantities of pale, fatty faeces and weight loss.  Since dogs with EPI have reduced functional pancreatic tissue, less trypsinogen is produced and therefore TLI blood tests result in low levels of serum TLI.

What does the test involve?

All that is necessary is a single, fasting (i.e no breakfast!) blood sample which is sent to a veterinary referral laboratory.

Is the test accurate?  Do all dogs with EPI have decreased TLI?

By the time the clinical signs of EPI are apparent, most dogs show significantly reduced levels of trypsin.  However, if the dog also has pancreatitis or if the sample is taken shortly after a meal, the amount of TLI may be temporarily increased and we may advise re-testing.

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