Function testing seeks to determine whether or not the pancreas is working normally. The three functions of the pancreas are to produce enzymes for digestion, to produce bicarbonate to neutralize gastric acid, and to produce insulin to signal cells in the body to begin taking nutrients out of the blood in anticipation of digestion and absorption of food.
The major test include:
- Enzyme secretion testing
- Bicarbonate secretion testing
- Insulin secretion testing
Enzyme secretion testing
The most accurate way to test for enzyme secretion is direct function testing. The method is to place a hose, tube or catheter at, on into the pancreatic duct, and measure pancreatic secretion for a about 90 minutes (depending on the test) after stimulating the pancreas with a hormone (e.g. CCK) or a test meal. The problem of this test is that it is difficult and expensive.
The most popular test in clinical practice is the human fecal elastase-1 test on stool samples. This test measures one of the digestive enzymes that is normally secreted by the pancreas. The advantage is that it is more convenient and less expensive, but it is not very sensitive, and only detects patients with more severe pancreatic dysfunction.
The 72 hour fecal fat test measures the body’s ability to digest fat during three days of a high-fat diet and stool collection for measurement of fat. The difference between the amount that goes in the mouth and that comes out the bottom is called the coefficient of fat absorption (CFA). This test is not so good for diagnosing pancreatic dysfunction, but is useful in proving that pancreatic enzyme replacement therapy (PERT) is effective in helping to digest fat in time for absorption, and therefore improve the CFA.
Bicarbonate secretion testing
Bicarbonate secretion testing is done to diagnose chronic pancreatitis. This must be done using a hose, tube or catheter that is placed at the location where the pancreas empties juice into the intestine. The pancreas is stimulated with secretin (e.g. ChiRhoStim) and the juice is collected for analysis. The amount of fluid that is secreted is not as important as the concentration of bicarbonate, which should be > 80 mEq.
Insulin secretion testing
Insulin secretion from the pancreatic islet cells is critical for maintaining normal blood sugar. In most clinical cases, insulin levels are not measures. Rather, the physician works on diet and medicines to keep the blood sugar in normal ranges. In several studies about half of the patients with chronic pancreatitis went on to develop diabetes mellitus from loss of insulin-making islet cells.