What should you know about an IgG blood test for food intolerance?

IgG antibodies can be detected after the immune system has encountered foods. Detection does not show that a food is causing digestive symptoms. Food intolerance is often considered when symptoms follow a food without the typical rapid allergic pattern, but symptoms such as bloating, cramps and diarrhoea have numerous possible causes.

A clinician may ask about meals, timing, stool changes, medicines, stress, previous diagnoses and any weight change. The result should be interpreted as one small piece of information, not as a list of confirmed intolerances. Coeliac disease and other bowel conditions may need consideration before changing gluten or other foods.

Use a diary to record meals, portions and symptoms for a limited period. Bring the IgG report and diary to a clinician, who can decide whether targeted food intolerance testing or another evaluation is suitable. If a food trial is advised, agree how long it will run and how reintroduction will happen. Nutrition counselling can help prevent deficiencies when several foods seem troublesome.

Seek prompt medical advice for ongoing diarrhoea, blood or black stool, repeated night-time symptoms, fever, dehydration, persistent vomiting or unexplained weight loss. Emergency care is needed for severe pain with collapse, confusion or inability to keep fluids down. The test result does not determine urgency; the symptoms do.

Ask what else could explain the symptoms, whether testing should happen before dietary restriction, how to judge improvement, and how to maintain adequate fibre, energy and nutrients during any food trial.