Trypsin and chymotrypsin

What is being tested?
Trypsin and chymotrypsin are proteolytic enzymes. Their job is to digest proteins in the small intestine. Normally their precursors (inactive forms: trypsinogen and chymotrypsinogen) are made in the pancreas and carried to the small intestine. There, trypsinogen is activated into trypsin by an enzyme in the intestinal lining, and trypsin in turn activates chymotrypsinogen into chymotrypsin. Together they are powerful chemicals responsible for breaking down food proteins into smaller parts called peptides. Trypsin and chymotrypsin will be present in the small intestine and in the stool if the pancreas is working normally.

In people with cystic fibrosis, mucus plugs can block the pancreatic ducts leading to the small intestine, preventing trypsinogen and chymotrypsinogen from reaching the intestine. Similarly, mucus plugs can block the small airways in the lungs, making the person susceptible to respiratory infections and chronic lung disease. It is usually the respiratory complications of cystic fibrosis that eventually prove fatal for the patient.

People with pancreatic dysfunction (tissue damage or blockage) may have either blocked pancreatic ducts or damaged or destroyed cells that produce trypsinogen and chymotrypsinogen. This cell damage causes pancreatic insufficiency, in which the delivery of enzymes to the small intestine is inadequate for normal food digestion. This is often seen in conditions such as chronic pancreatitis and pancreatic cancer.

How is the sample collected for testing?
A fresh stool sample, not contaminated with urine, is collected. For a young child, a urine collection bag with adhesive edges attached to the child’s skin and a plastic-lined nappy are used to keep the urine separate from the stool and to stop the stool soaking into the nappy.

How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?

How is it used?
The trypsin/chymotrypsin test is used to screen newborns and symptomatic children for cystic fibrosis and to assess children and adults for pancreatic insufficiency.

When is it requested?
The trypsin/chymotrypsin test is easy and non-invasive. It is requested when a newborn or child has symptoms of cystic fibrosis, such as persistent diarrhoea, fatty, bulky, foul-smelling stools, malnutrition and vitamin deficiency. It is also requested when a child or adult has these symptoms, to help diagnose pancreatic insufficiency.

What does the test result mean?
A positive result showing trypsin and chymotrypsin in the stool is normal. A negative result is not diagnostic but indicates that further tests may be needed for either pancreatic insufficiency or cystic fibrosis. Other pancreatic disorders, such as acute and chronic pancreatitis, can cause negative results.

Is there anything else I should know?
If a person’s pancreas is not working properly, they will need to be closely monitored by their doctor. They may then get relief from symptoms and improve their nutrition by taking oral enzymes and vitamin supplements prescribed by the doctor.

1. What other test might the doctor do to check for cystic fibrosis?
2. What other laboratory tests can be done if I or my child have a negative trypsin test?

1. What other test might the doctor do to check for cystic fibrosis?
The doctor may request the immunoreactive trypsinogen (IRT) test, the sweat chloride test and/or the CF gene mutation test.

2. What other laboratory tests can be done if I or my child have a negative trypsin test?
The doctor may request a stool test for faecal fat or a blood test for amylase and lipase to look at other aspects of pancreatic and digestive function.