Lactose and Dairy Intolerance Testing

Reacting badly to milk, cheese or cream is common, but the reason behind it varies from person to person. "Dairy problem" can mean two quite different things — a true milk allergy or lactose intolerance — and telling them apart matters, because they are managed very differently and carry very different risks.

Two different conditions

It helps to be clear about what is actually going on:

• Milk allergy — an immune reaction, driven by IgE antibodies, to the proteins in milk. It can cause hives, swelling, wheezing, vomiting and, in severe cases, a serious whole-body reaction. It is more common in young children but can persist or, rarely, appear later.
• Lactose intolerance — not an allergy at all, but a shortage of lactase, the enzyme that digests the milk sugar lactose. Undigested lactose ferments in the gut, causing bloating, wind, cramps and loose stools, typically a while after eating dairy. It is uncomfortable but not dangerous.

What the blood test covers

An IgE blood test for milk and dairy measures antibodies to milk protein. This is the relevant test when a true milk allergy is suspected — for example where reactions are rapid or involve the skin or breathing. A positive result, interpreted alongside your history, supports an allergy diagnosis and helps guide safe avoidance.

How lactose intolerance is assessed

Lactose intolerance is not diagnosed by an IgE allergy test. It is usually identified through the pattern of symptoms in relation to dairy, sometimes supported by a hydrogen breath test or a supervised trial of removing and then reintroducing lactose. Because dairy is a valuable source of calcium and other nutrients, it is best to make changes with guidance rather than cutting it out entirely on a hunch — lactose-free products and hard cheeses are often tolerated well.

Focused panels for the most common suspects

The dairy panel above covers milk in all its forms — cow's, goat's and sheep's milk, casein and several cheeses. If milk is only one of several suspects, or you want the classic childhood trio checked together, the Egg, Milk & Wheat panel does that in one test. Three further focused panels cover the non-food triggers whose symptoms are sometimes blamed on dairy. Each tests four allergens plus Total IgE and costs £143:

For a single food not on any panel, type it into the search box on the booking page and build a custom allergy test from any of 185 individual allergens, from £99 for two. All of these are IgE allergy tests: none of them, and no blood test, diagnoses lactose intolerance.

Which points to which

As a rough guide, rapid symptoms affecting the skin, mouth or breathing point towards allergy, while slower digestive symptoms — bloating, wind and loose stools an hour or two after dairy — point towards lactose intolerance. In reality the picture can overlap, which is why a clinician's assessment of your symptoms is so valuable in choosing and interpreting the right test.

When to seek prompt advice

Seek urgent medical help if you have ever had a sudden, severe reaction to dairy — swelling of the lips, tongue or throat, difficulty breathing, or faintness — as this suggests a significant allergy needing an emergency plan. You should also see a doctor if dairy-related symptoms come with red flags such as unexplained weight loss, blood in your stool or persistent vomiting, which need proper assessment rather than dietary guesswork.

Written by Dr Ibrar Ahmed — MBChB MRCP MRCGP PhD PG Dip (Cardiology)
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic