What every parent must know about allergy testing

How to Test Children for a Suspected Milk Allergy
Written by Registered Dietitian Nishti

We are often asked how to test children who may have a cow’s milk protein allergy—or an allergy to other foods.

Before we get into testing, it’s essential to understand the type of allergy we are dealing with. There are two main types of cow’s milk allergy:

1. IgE-mediated (immediate reaction)

2. Non-IgE-mediated (delayed reaction)

Each type presents with different symptoms and requires a different approach. If you're not sure which applies to your child, we recommend reading this blog first for a full explanation of the differences.

Validated Tests for IgE-Mediated Allergies

Testing can be helpful—but only for IgE-mediated allergies. Even then, tests alone cannot confirm a diagnosis. An allergy-focused history taken by a qualified healthcare professional is crucial and always comes first. Testing should only be done if there is a clinical reason to suspect an IgE-mediated reaction.

There are only two validated tests for IgE allergies:

• Skin Prick Test (SPT): Results are available in about 20 minutes.

• Specific IgE Blood Test (sIgE): Results usually take a few days.

With SPT, a larger wheal size typically indicates a higher likelihood of an allergy—but it does not predict how severe a reaction will be.

📺 Watch: Nishti explains allergy testing in this ITV News clip.

Why Testing Doesn’t Work for Delayed Allergies

If your child has a delayed (non-IgE) allergy, testing is not useful. There are no validated tests for this type of allergy. Instead, the gold standard for diagnosis is an elimination and reintroduction diet:

1. Remove cow’s milk protein from the diet for 2–4 weeks.

2. Observe if symptoms improve.

3. Reintroduce milk to see if symptoms return.

This is the only reliable method for identifying non-IgE allergies.

What Allergy Tests Can—and Can’t—Tell You

• ✅ Tests can help identify the likelihood of a reaction.

• ❌ Tests cannot predict how severe the reaction will be.

• ❌ Tests cannot detect non-IgE (delayed) allergies.

If Your Child Has Immediate Reactions

If your child shows signs of an immediate reaction to milk or other foods (e.g., hives, vomiting, breathing difficulty within minutes), they must be referred to a consultant in allergy. 

References

• Fox, A., Brown, T., Walsh, J. et al. (2019). An update to the Milk Allergy in Primary Care guideline. Clin Transl Allergy, 9, 40. https://doi.org/10.1186/s13601-019-0281-8

• Luyt D, Ball H, Makwana N, et al. (2014). BSACI guideline for the diagnosis and management of cow’s milk allergy. Clin Exp Allergy, 44(5), 642–672. https://doi.org/10.1111/cea.12302