Assessing the exocrine activity of the pancreas can be done with a number of pancreatic function tests. This range of laboratory tests will require blood, stool and/or intestinal secretions to detect the presence of pancreatic digestive enzymes.
Malabsorption can be determined by testing the blood for deficiencies or the stool for the presence of nutrients that should have been digested and absorbed within the gut. However, this type of nutrient testing is not always indicative of pancreatic insufficiency and could be due to a host of other causes that result in malabsorption.
Types of Pancreatic Exocrine Function Tests
Tests for pancreatic enzymes in the blood, stool, intestinal secretions.
- Secretin stimulation test
- Fecal elastase
- Pancreolauryl test
- Benitromide test (BT-PABA)
- Serum trypsinogen test
- Fecal chymotrypsin
Secretin Stimulation Test
The secretin stimulation test is the gold standard. However, it is invasive and therefore not conducted frequently.
The secretin stimulation test is conducted by inserting a tube down the mouth, past the esophagus and stomach and into the duodenum (duodenal intubation). Secretin is then administered into the small intestine. This digestive hormone stimulates bicarbonate and water secretion from the pancreatic ducts which carries digestive enzymes out of the pancreatic acini and it also neutralizes acidic stomach chyme. The intestinal secretions are collected and analyzed over a period of 2 hours.
Fecal Elastase Test
In this test, a stool sample is analyzed (immunoassay) for the presence of elastase. This will indicate whether the pancreas is secreting digestive enzymes. It is preferred over the secretin stimulation test in that it avoids duodenal intubation, however, it is may not detect mild exocrine pancreatic insufficiency.
Fluoroscein dilaurate is administered orally and the pancreatic esterases (lipid digestive enzymes) should cleave it. Lauric acid is then passed out in the urine. It is accurate and preferable in that it avoids intubation. However, one of the drawbacks is that urine has to be carefully collected over a period of two days.
Also known as the bentiromide test, it involves the oral administration of the peptide bentiromide. The metabolites of this compound is then analyzed in the urine and provides an indication of the presence and activity of pancreatic peptidase (protein digestive enzymes). However, it is not conducted in some countries due to side effects.
Serum Trypsinogen Test
A blood sample is collected and analyzed for trypsinogen, the precursor of trypsin which is one of the main proteases in pancreatic enzymes. Elevated levels of trypsinogen may be indicative of conditions like acute pancreatitis, pancreatic cancer and cystic fibrosis. Normal or low levels may be seen in chronic pancreatitis.
Fecal Trypsin/Chymotrypsin Test
A stool sample is analyzed for trypsin or chymotrypsin. The presence of these enzymes (positive result) in the stool is normal but if absent (negative result), pancreatic insufficiency related to cystic fibrosis, acute or chronic pancreatitis should be suspected and investigated further.
Stool Tests for Nutrient Malabsorption
- The most common of these tests is the fecal fat test. This is used to identify lipids in the stool which results in steatorrhea.
- A test for the presence of proteins in the stool (creatorrhea) may also be conducted but should be further assesed for the type of protein. Larger serum proteins are seen in protein-losing enteropathy rather than in malabsorption.
- Carbohydrates in the stool can be detected by the presence of reducing substances and also assessed by stool pH. Acidic stool (pH <5.5) is indicative of carbohydrate malabsorption.
None of these stool tests are conclusive for exocrine pancreatic insufficiency as there are various causes of malabsorption. Pancreatic function tests, as mentioned above, should be conducted to confirm the diagnosis.