Gut
Tryptofaan
A building block of protein that is measured in the stool; the meaning for health has not been established.
Everything about this testWhat it measures
Tryptophan is an amino acid, a building block of protein, that the body cannot make itself and gets from food. It is normally absorbed in the small intestine. Gut bacteria convert tryptophan that reaches the large intestine into other substances. The laboratory measures how much tryptophan is in a stool sample.
- A sign of incompletely absorbed protein or fast passage through the gut; the meaning has not been established
High
A raised value can be caused by a protein-rich diet or fast passage through the gut, so that protein and its building blocks are not fully absorbed. There is no condition for which this measurement in stool is used to make a diagnosis. The result says nothing about the amount of tryptophan in the blood or in the brain.
Low
A low value means little tryptophan in the stool and fits good absorption of protein. A low value does not mean that you get too little tryptophan or have a deficiency, and has no known meaning for mood or sleep.
If your result is abnormal
Without symptoms, an abnormal result from this test usually needs no follow-up. With symptoms that fit poor digestion, the GP can request pancreatic elastase in the stool or a blood test for celiac disease, and if needed refer you to a gastroenterologist or internist (specialist in internal medicine).
Reliability
Food remnants in a single stool sample mainly say something about what you have eaten and how quickly the food passed through the gut. How well the result shows or rules out poor digestion has not been well studied, neither in people without symptoms nor in people with bowel symptoms. If poor fat digestion (malabsorption) is suspected, the specialist may have fat measured in stool collected over a few days. For pancreatic function, pancreatic elastase in the stool has been studied better.
Limitations
- Food in the days before sample collection (fat, meat, raw vegetables, legumes, dairy, sugars) largely determines the result.
- Diarrhea or, on the contrary, constipation changes the result, because the speed through the gut determines how much is digested.
- One stool sample gives a snapshot; the composition differs from day to day.
- Medicines such as laxatives, antibiotics, stomach acid inhibitors, pancreatic enzymes and weight-loss medicines that block fat absorption (orlistat) affect the result.
How common is this
There are no Dutch figures on how often an abnormal result for these tests occurs. Bowel symptoms themselves are common: according to the guideline, irritable bowel syndrome affects about 4 in 100 adults. Conditions in which food is truly poorly digested, such as chronic inflammation of the pancreas, are much rarer.
Who is this useful for
Because diet strongly determines the result, this test says little in people without symptoms, and even with symptoms it does not identify a cause. With symptoms that may fit poor digestion, such as long-lasting fatty or mushy stools, unintended weight loss or long-lasting diarrhea, testing through the GP is the right route. Pancreatic elastase in the stool and a blood test for celiac disease are then more targeted first tests. With blood in the stool, unintended weight loss or new bowel symptoms after the age of 50, this test is no substitute for a visit to the GP.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results