Unfortunately there are no tests that provide information that gives you a clear diet direction in IBS. That is because there is no clear physiological mechanism known to be at fault in IBS. Diet options for IBS is still a new area for dietetics. It is rather like diet and migraine, another symptom where the problem physiological mechanism is not known. From my clinical research they are both symptoms that occur in food sensitive people. Another symptom is eczema which does have some allergic part. So allergy tests can be helpful with eczema though often not the full solution.
Thinking back over my clinical research I have only rarely had IBS patients who had an allergic reaction with their IBS. Where it occurs they often report, for example, that they are allergic to some food that gives them hives or some of the usual allergic symptoms. But staying away from a known allergen has no affect on IBS symptoms. What can you do? You have foods you suspect so you may look on the internet and try diets suggested eg milk or wheat free, low histamine or low tyramine, or being additive free, low chemical, and many others. Or your doctor may suggest a diet direction. If you want to work out a diet for yourself you can look at my suggestion below. If you want to ask “Is food intolerance is an inborn error of metabolism?”, or when “Thinking about cures for food chemical sensitivity symptoms” you can look at in the Articles section on my site https://foodintolerancepro.com/articles/
Imagine if you worked with allergic condition before allergy tests were available. You might leave out all the foods most often reported to obviously aggravate symptoms – the usual suspects: dairy, wheat, fish, shellfish, soy, nuts and others – and you may have symptoms improve. Then you would very carefully gradually challenge with each of the exclusions and see which one, at which amount, produced symptoms. Gradually you would produce the diet for yourself or your child.
We are at that same point of not having useful tests for IBS or for any of the other conditions that respond to the Low Chemical Diet. Many people, including me, have been looking for over 40 years now. We do know that allergy tests do not help with IBS. What foods are most often reported as aggravating symptoms here? I have the list on p 25 of my book Your Diet for Your IBS.
Some work has been done on the Low FODMAPs Diet so some gastroenterologists recommend it, but it may reduce some symptoms or even worsen some so it is often not the full solution. Some in the US use the LEAP tests but I note that dietitians still individualise it, and challenges are needed so dietetic supervision is still wise. Using my book Your Diet for Your IBS you can find the best elimination diet to begin with and be guided through your own preferred challenge foods.