The food intolerance blood test you paid for doesn't work. Here's why.

What the test actually measures

Your immune system makes several classes of antibody. Two matter here, and they are easily confused because the names differ by one letter.

IgE is the antibody of true, immediate allergy. It is what causes hives, swelling, vomiting and anaphylaxis within minutes of eating something. Testing for specific IgE — by blood test or by skin prick — is a legitimate, well-validated part of allergy diagnosis.

IgG is a different antibody entirely, and making it against a food is a normal response to eating that food. It is a record of exposure. Some evidence suggests IgG4 in particular is associated with tolerance — that is, with the body having got used to something. So a panel showing "high IgG to wheat, milk and rice" in an Indian patient is very often just a description of their diet.

What the allergy bodies say

This is not a minority view or a matter of opinion. The American Academy of Allergy, Asthma & Immunology's first Choosing Wisely recommendation reads: "Don't perform unproven diagnostic tests such as immunoglobulin G (IgG) testing or an indiscriminate battery of immunoglobulin E (IgE) tests in the evaluation of allergy." Their stated reason is that specific IgG testing does not indicate allergic conditions.

Allergy UK is equally direct: there are many tests available that are not validated by science or recommended by allergists — including vega testing, hair analysis and blood tests that do not look for IgE — and such tests are not recommended, as they may give false readings.

Note the second half of the AAAAI sentence, which gets less attention: an indiscriminate battery of IgE tests is also advised against. Ordering a 120-allergen panel on someone who has not been asked a single question about their symptoms produces a list of positives with no meaning. The test is chosen after the history, not instead of it.

Why it isn't harmless

The money spent is the smallest part of the harm. What follows is a list — often twenty or thirty foods — and a family who dutifully removes all of them. In children this can mean a diet stripped of milk, wheat and egg during the years of fastest growth, with real consequences for nutrition and for the child's relationship with food.

There is a subtler harm too. Prolonged avoidance of a food someone was tolerating can, in some cases, make a genuine allergy more likely on reintroduction. And while the family is managing a list of imaginary intolerances, the actual cause of the symptoms — reflux, coeliac disease, lactose intolerance, irritable bowel, or a real IgE-mediated allergy to one specific food — goes unexamined.

What we do instead

• The history first. What was eaten, how much, how long afterwards symptoms began, what the symptoms were, whether it has happened more than once, what else was going on. Minutes points to allergy; hours to days points elsewhere.
• Skin prick testing or specific IgE to the small number of foods the history actually implicates — not a panel of everything.
• Component-resolved testing where it changes the answer, for example distinguishing a peanut protein associated with severe reactions from one associated with mild ones.
• A supervised oral food challenge where the picture stays unclear. This remains the gold standard. It is done with medical supervision and resuscitation facilities, never at home.
• An honest "this is not an allergy" where that is the answer, with a plan for what it might be instead.

If you have already had one

You are not foolish for having had this test. It is sold confidently, sometimes by laboratories and sometimes by doctors, and the marketing is persuasive. Bring the report. It is worth going through, because knowing which foods you removed, and when your symptoms actually changed, is genuinely useful information — and the reintroduction is safer done with a plan than on your own.

Next step

Get the right test instead

Send your existing reports on WhatsApp before you come — it means more of the appointment is spent on you and less on paperwork.