- test for cystic fibrosis (CF), as part of a routine screening of infants
- test infants with symptoms of CF, who do not produce enough sweat for a sweat chloride test
- test for pancreatic insufficiency in both children and adults who have symptoms consistent with this condition
When food enters the small intestine, the pancreas is stimulated to release a fluid containing inactive digestive enzymes (which help break down fats, carbohydrates, and proteins) and bicarbonate (a base that helps neutralize the acid entering the small intestine). A duct carries this pancreatic fluid into the upper portion of the small intestine (the duodenum). The bicarbonates then neutralize the stomach acids, allowing for the activation of the digestive enzymes.
One of these inactive enzymes is called trypsinogen. Its active form is called trypsin. This enzyme breaks proteins into amino acids so that the body can use them as nutrients.
Certain diseases can interfere with this process. This condition is called pancreatic insufficiency. Pancreatic insufficiency may be caused by (for example) cystic fibrosis (CF), pancreatitis, or pancreatic cancer.
The test for trypsinogen can be used as part of the process of diagnosing these diseases, but it will not be enough alone. Other tests will be necessary to complete the diagnosis.
A trypsinogen test is normally conducted to:
People with CF may develop mucus plugs in their pancreatic ducts, preventing pancreatic fluid from reaching the duodenum.
People with pancreatitis or pancreatic cancer may have tissue damage that blocks pancreatic ducts. They may also have damage to the cells that produce trypsinogen. In either case, trypsin will not be available in sufficient quantities to digest proteins in the small intestine.
No preparation is necessary for this blood test.
A heel stick is used to get a blood sample from infants. This is a procedure involving a small heel-lancing device that allows a doctor to safely take a small blood sample from an infant. The test area will be cleaned with an antiseptic prior to the test. A bandage may be applied afterwards to stop bleeding.
In adults, blood is taken from a vein in the inner elbow. This is called a venipuncture. The technician will clean the test area with an antiseptic and wrap an elastic band around the upper arm to make the vein swell. Then the needle is gently inserted, and blood flows into a tube. When the tube is filled, the technician will remove the elastic band and then the needle. A bandage may be placed over the area where the needle was inserted.
Normally, there is some pain when the needle is inserted and some throbbing afterwards.
Some people don’t like needles. It can be helpful to ask for ice to be applied to the area where the needle is to be inserted. This will numb the area to some extent.
The trypsinogen test alone is not enough to diagnose any of the diseases mentioned above. If the test is positive, it could be an indication of CF or pancreatic insufficiency. But there are often false positives, and other tests will be needed to confirm a diagnosis.
Serum amylase and serum lipase are among the other tests that can also be used to diagnose diseases of the pancreas.
If an infant has symptoms of CF, but the trypsinogen test is negative, other tests should be considered.
Sometimes an abnormal production of pancreatic enzymes will also give abnormal results.