There are circumstances when perhaps the parents of your patient have already empirically placed their child gluten free without having a small bowel biopsy performed and have found an improvement in their child’s symptoms. This could be due to their child genuinely having coeliac disease. But other possibilities exist, such as wheat intolerance, a problem with FODMAP foods (which commonly have gluten in them). They may have an irritable bowel type syndrome. It could also be co-incidental or there could be a placebo effect.
Normally we would recommend a gluten challenge to definitively diagnose coeliac disease. We would also do HLA DQ2 and 8 testing to determine if they are at genetic risk for coeliac disease, because if they lack the DQ 2 or 8 alleles, then it becomes highly unlikely that they have coeliac disease or will develop it. The DQ2 and 8 testing can be done even if the patient is gluten free. Doing coeliac serology (tTG-IgA or DGP) while they have been off gluten is not useful, unless this has happened within the past few weeks. The planning of a gluten challenge needs to be done in conjunction with discussing it with your paediatric gastroenterologist, so that a date for doing the small bowel biopsy can be tentatively arranged, in order to minimize the duration of gluten exposure.
If the patient shows a positive DQ2 or 8 allele, then they should undergo a gluten challenge. The duration of the challenge varies, but we would generally recommend (in children) 1-3 slices of bread/day or the equivalent, depending on their age, for at least 4 weeks. Sometimes the return of symptoms can be very rapid, but sometimes it can be delayed, and so you would need at least 4 weeks of symptoms before considering a biopsy. Some children are not able to continue with the challenge because their symptoms become too severe, and the challenge has to be stopped after discussion with your gastroenterologist.