The pancreas is a glandular organ located close to the liver, the stomach, and the small intestine. It functions in the control of blood glucose (sugar) through the secretion of insulin and glucagon hormones, and aids in digestion through the secretion of lipase and amylase enzymes.
What types of pancreatic disease may occur?
Pancreatic disease can be broadly classified as disease related to the exocrine portion of the pancreas; that is, disease related to the enzymes associated with the digestive functions of the pancreas, and as disease related to the endocrine portion of the pancreas; that is, disease related to the control of blood glucose.
Other pancreatic diseases include pancreatitis and pancreatic tumors.
Pancreatitis is generalized inflammation of the pancreas. The underlying cause of pancreatitis is often not known, but it may be related to the recent consumption of a fatty meal, to the administration of corticosteroids, or to direct trauma to the pancreas. Depending upon the degree of inflammation, there may be long term effects with respect to either the exocrine or endocrine pancreatic functions.
Rarely, tumors of the pancreas may occur. These tumors usually involve the pancreatic beta cells (these cells manufacture insulin), but other tumors of the pancreas may also occur.
How do we test for these pancreatic diseases?
The clinical signs that your pet exhibits give us the first ‘clues’ that exocrine pancreatic disease might be present. Disease of the exocrine portion of the pancreas causes insufficient production of the enzymes required for proper digestion of fats, carbohydrates, and proteins. This condition is termed exocrine pancreatic insufficiency. The patient with this problem usually produces large amounts of feces and shows gradual weight loss despite a good appetite.This condition can occur in dogs due to a previous episode of pancreatitis, or it may be a condition that is congenital or inherited. Certain breeds of dogs seem to be predisposed to developing this problem.
The most sensitive and specific test for diagnosing exocrine pancreatic insufficiency is determination of the trypsin-like immunoreactivity (TLI) of a serum sample. This involves taking a single, fasting blood sample that is sent to a veterinary referral laboratory for TLI determination.
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 is involved in the digestion of proteins. In healthy animals, a small amount of trypsinogen escapes from the pancreas into the blood, where it can be measured in the TLI test.
Dogs with exocrine pancreatic insufficiency have reduced functional pancreatic tissue, and consequently less trypsinogen is produced. Therefore less trypsinogen escapes into the circulation, resulting in low levels of serum TLI.
Do all dogs with 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 tests that may be used to diagnose exocrine pancreatic insufficiency?
Yes but these tests have been largely replaced by the trypsin-like immunoreactivity test.
Determination of B12 (cobalamin) and folate concentrations in a serum sample may provide supportive evidence of exocrine pancreatic insufficiency. Dietary deficiency in either of these two vitamins is unlikely since they are readily available in most commercial diets. However, because pancreatic digestive enzymes are required for the proper absorption of B12 from the digestive tract, exocrine pancreatic insufficiency may result in decreased serum concentrations of B12. Folate concentrations may be increased in serum samples from dogs with exocrine pancreatic insufficiency because intestinal bacterial overgrowth accompanying the insufficiency results in increased bacterial production of folate.
Endocrine pancreatic disease testing
The endocrine portion of the pancreas functions to regulate blood glucose. This is accomplished primarily through the effects of the hormones insulin and glucagon. A deficiency in insulin results in diabetes mellitus (sugar diabetes). Testing for diabetes mellitus is discussing in the handout entitled “Testing and monitoring diabetes patients”.
Testing for pancreatitis
Inflammation of the pancreas (pancreatitis) may occur due to many factors. In addition to clinical signs that may include vomiting, fever, and abdominal pain, there are some characteristic laboratory changes that support a diagnosis of pancreatitis.
The CBC (complete blood count) may reveal an increase in the number of white blood cells due to the inflammation within the gland. Also, the PCV (packed cell volume), which is an indication of the total mass that the red blood cells are occupying in circulation, may be increased because of dehydration.
The serum biochemistry profile may reveal increases in the pancreatic enzymes amylase and lipase. Amylase and lipase are enzymes involved in the digestion of starches and fats, respectively. Normally these enzymes are not active until they are secreted into the digestive tract, but with pancreatitis they become prematurely activated and cause damage within the pancreas.
This premature enzyme activation and leakage also results in increased amylase and lipase concentrations in the serum. Although the increases in amylase and lipase can be variable, they are often quite dramatic.
Are these tests definitive for pancreatitis?
No. Any inflammatory condition may cause white blood cell numbers to become increased. Similarly, any condition resulting in dehydration can cause an increase in the PCV. Conditions that have been shown to cause mild increases in amylase and lipase include kidney disease, neoplasia (cancer), gastrointestinal disease, and liver disease.
Therefore, in addition to providing information about the pancreatic enzymes, a serum biochemistry panel will give additional information about the function of these other organs to help rule them in or out as contributors to the increase in pancreatic enzymes.
Some animals, especially cats, despite having strong clinical evidence of pancreatitis will not have significant increases in lipase or amylase enzymes in a serum sample.
Are there any other tests that may be used for the diagnosis of pancreatitis?
Trypsin-like immunoreactivity has been occasionally used for the diagnosis of pancreatitis. An increased amount of trypsin or trypsinogen may be released from damaged pancreatic cells during a bout of pancreatitis, resulting in increased blood concentrations. However, trypsin-like immunoreactivity is not reliably increased with pancreatitis and measurement requires that a serum sample be sent to a veterinary referral laboratory. Obviously this is not convenient in clinically urgent situations.
Occasionally other procedures such as ultrasound evaluation of the abdomen are helpful in the diagnosis of pancreatitis, when laboratory testing fails to provide a definitive answer.