Symptoms are not a reliable way to determine gluten exposure, but urine and stools tests might help
By Amy Ratner, director of scientific affairs
In children with celiac disease, it can be a challenge to connect the dots between any gluten getting into the child’s diet and the consequences, especially if the child does not have any symptoms.
In a recent study, Boston researchers set out to determine if tests that measure gluten in urine and stool can be used as markers of gluten exposure in children on the gluten-free diet.
The study found that children with celiac disease who had detectable amounts of gluten in their urine and stool did not have any symptoms. However, overall, the number of children with detectable immunogenic protein (GIP) in urine and stool samples was small, the study says. GIPs are fragments of gluten proteins that are resistant to digestion by enzymes in the gastrointestinal tract.
The study supports previous research that shows symptoms are not a reliable way to determine if a child has been exposed to gluten, the authors note. A 2016 study found that one in five children with celiac disease may not heal despite following the gluten-free diet for at least a year, with neither positive results of celiac disease blood tests nor symptoms being reliable predictors of intestinal damage.
Meanwhile, none of the children in the new study who had persistent damage to the intestine had detectable levels of gluten in urine samples taken at the time they had endoscopies done.
In the multicenter collaboration by Massachusetts General Hospital and Boston Children’s Hospital, scientists tested at least one urine sample from 84 children and at least one stool sample from 22. Study participants ranged from six to 21 years, and all had been on the gluten-free diet for at least 6 months. Seventy percent of study participants reported that they had no symptoms. Most study participants provided a single sample.
The samples were collected in three settings: a facility where children were having an endoscopy, a gastroenterology clinic and in the study participants’ homes. This is the first time testing children at home was evaluated. The researchers wanted to investigate the tests in real world settings, they note.
The authors concluded that more research is needed to understand the range of gluten excretion in children and how specific and sensitive testing is before the tests can be used to give rapid results in a doctor’s office, clinic or other medical care setting.
Currently, how well a child is following the gluten-free diet is determined by a dietitian’s evaluation of the child’s diet, questionnaires, blood tests for antibodies to gluten and symptoms. Study authors called this method “highly subjective and notoriously inaccurate.” They set out to determine if tests for GIP in urine and stool could provide an objective and non-invasive way to determine if gluten is getting into a child’s diet.
Detectable GIP was found in about 9 percent of 44 stool samples and about 5 percent of 125 urine samples.
These rates were low compared to earlier adult and pediatric studies conducted in Europe, which reported a 13 percent to 24 percent rate of GIP in stool and a 5 percent to 38 percent in urine. All the children who participated in the Boston study came through specialized celiac centers where 93 percent were counseled on the gluten-free diet. This dietary education might have improved adherence to the gluten-free diet, the study says.
Although repeat sampling is more likely to detect gluten, the study was designed to evaluate how practical it would be to screen for gluten in a doctor’s office or other medical setting where a single sample collection is preferable. The study authors acknowledged that the timing of GIP excretion after gluten is consumed is also a potential detection limitation. The window for detecting gluten in stool is longer than urine, 24 to 72 hours compared to 3 to 6 hours, the study says.
For children in the study who had persistent intestinal damage revealed through a biopsy but no evidence of GIP in urine, the authors suggest these study participants may have been ingesting enough gluten to trigger inflammation but an amount that was below the level of detection of the urine test.
The amount of gluten needed to trigger intestinal damage is not well-defined and is known to vary, the authors note.
Alternatively, subjects might have changed their diet in the short-term, avoiding gluten in the days leading up to the endoscopy even though they did not know that testing for gluten in urine was going to be done. Long-term gluten exposure might have been the trigger for the persistent intestinal damage found in biopsies, the study says.
Other research has found that nearly 100 percent of study participants who had intestinal damage had GIP in urine samples.
Testing of multiple urine samples for GIP could potentially make the tests more useful when used to detect gluten exposure in those who have persistent intestinal damage found through an endoscopy and biopsy, the study says.
Study limitations include the small number of samples and the limited number of multiple samples from all study participants. The authors note that it was more difficult for study participants to collect samples in some settings than others, which will be useful to know for future research. Future research will also benefit from general sampling recommendations since there is variation in the dynamics of gluten absorption and excretion, the study says.
This “will help clarify the interpretation of positive and negative GIP results across all collection settings,” the study concludes.
Glutenostics, the company that sells the urine and stool tests in the United States, sponsored the study.
You can read more about the study here.