Blood test to see food intolerance: what to know

Food intolerance describes symptoms after eating a food without the same immune mechanism seen in many food allergies. Clinicians usually consider timing, portion size, repeated patterns and other explanations. Some blood tests look for signs of allergy or related conditions, while tests marketed as broad intolerance panels may not provide a reliable diagnosis. Symptoms such as bloating or diarrhoea can have many causes and do not identify one food on their own.

Keep a simple food and symptom diary, including ingredients, timing and how long symptoms last. Do not remove several foods for a long period without professional advice, because this can reduce nutritional variety and make the pattern harder to interpret. A clinician may suggest a planned elimination followed by reintroduction, or another targeted investigation. A registered dietitian can help protect your nutrition during this process.

Seek urgent help for swelling of the lips or tongue, trouble breathing, faintness or a rapidly spreading itchy rash after eating. Arrange medical review for persistent diarrhoea, blood in the stool, repeated vomiting, unexplained weight loss or symptoms that wake you at night. These features need assessment rather than self-testing.

Ask which reaction is being investigated, whether you need to continue eating the food before testing, and how a result would change your care. Ask whether your symptoms warrant assessment for another digestive condition and whether nutrition counselling would be useful.