Baby Allergy Testing UK: What to Expect at an Allergy Clinic

Food allergies in babies are increasingly recognised, and more parents than ever are seeking clarity on whether their child's symptoms — a rash, tummy trouble, persistent eczema — are related to a food allergen. If you are waiting for an NHS allergy referral or have been told your baby might need testing, here is a clear, practical guide to what the process involves.

When Does a GP Refer a Baby for Allergy Testing?

GPs do not routinely test babies for allergies without a clinical reason. A referral to a paediatric allergy clinic is typically made when:

• There has been a clear allergic reaction to a food, including hives, swelling, vomiting shortly after eating, or difficulty breathing
• Your baby has persistent eczema that does not respond to standard treatment, particularly if it flares after feeding
• Your baby is being breastfed and you have identified a pattern of reactions after you eat certain foods
• A cow's milk protein allergy (CMPA) is suspected based on symptoms such as blood in the stool, severe reflux, or failure to thrive despite treatment

Some mild reactions and suspected intolerances (as opposed to true IgE-mediated allergies) are managed in primary care without specialist referral, using dietary elimination trials under GP or dietitian guidance.

Types of Allergy Tests Available

Skin Prick Test (SPT)

This is usually the first-line test in a paediatric allergy clinic. A small drop of allergen extract is placed on the forearm or back, and a lancet is used to gently prick the skin through the drop. No blood is taken. The skin is then observed for 15 to 20 minutes.

A positive result is a raised, itchy wheal (a small bump resembling a nettle sting) of 3mm or more compared to a control. This indicates sensitisation to that allergen.

What SPT can and cannot tell you: A positive skin prick test shows that your baby has IgE antibodies to a specific allergen — they are sensitised. However, sensitisation does not always equal allergy. Some children are sensitised to allergens they can eat without any problem. The result must always be interpreted alongside the clinical history.

SPT can be done from a very young age, including in infants under one year, though the wheals may be smaller in younger babies.

Specific IgE Blood Test (RAST or ImmunoCAP)

A blood sample is taken and sent to a laboratory to measure the level of IgE antibodies to specific allergens. Results are graded on a scale (often described as RAST classes 1–6). Higher levels generally correlate with a greater likelihood of a clinical reaction, but again, the result must be read alongside symptoms and history.

Blood tests are sometimes preferred when:

• Your baby has severe eczema making SPT interpretation difficult
• Your baby cannot safely stop antihistamines (which interfere with SPT)
• The clinic does not have the specific allergen extract for SPT

Component Resolved Diagnostics (CRD)

This more specialised blood test looks at which specific proteins within a food your baby is sensitised to. For peanut allergy, for example, sensitisation to Ara h 2 is associated with a higher likelihood of severe reactions than sensitisation to Ara h 8. CRD is not routinely used for all babies but can help refine risk assessment.

Oral Food Challenge (OFC)

In some cases, the definitive test is a supervised oral food challenge in clinic. Small, increasing amounts of the suspected allergen are given and your baby is monitored closely for reactions. This is done in a setting with full resuscitation equipment and trained staff.

OFC is the gold standard for confirming or ruling out allergy, particularly when test results are ambiguous or when assessing whether a child has outgrown an allergy.

What Happens at the Allergy Clinic

Appointments are typically with a paediatric allergist or a specialist paediatric nurse with allergy training. The consultation will begin with a detailed history — the allergist wants to understand exactly what happened, how quickly symptoms appeared, and what they looked like. This history is often as informative as the test results themselves.

Testing is usually done on the same visit if appropriate. If your baby is on antihistamines, you will be asked to stop them for a specified period (often five days) before the appointment.

You will leave the clinic with:

• The test results and their interpretation
• An action plan detailing what to do if your baby has a reaction
• Information on which foods to avoid (and whether any related foods also need to be avoided)
• A prescription for an adrenaline auto-injector (such as an EpiPen or Jext) if a severe reaction is considered possible
• Guidance on reintroduction or challenge if appropriate

Managing Confirmed Allergies

A confirmed food allergy in a baby requires practical day-to-day management:

• Label reading: UK food labelling law requires the 14 major allergens (including peanuts, tree nuts, milk, egg, wheat, soy, fish, and shellfish) to be clearly highlighted on pre-packaged food.
• Cross-contamination: Allergen traces from shared utensils, preparation surfaces, and cooking oils can cause reactions.
• Nursery and childcare: You will need to provide the setting with an allergy action plan, and they should have staff trained in administering an EpiPen if prescribed.
• Dietitian support: If significant foods are excluded from your baby's diet, a referral to a paediatric dietitian helps ensure nutritional needs are still met.

NHS Waiting Times and Private Options

NHS allergy clinic waiting times vary considerably by area — some families wait several months. If the wait is long and you are concerned, ask your GP whether your baby's symptoms can be managed in primary care in the interim, or whether an urgent referral pathway applies.

Private paediatric allergy assessments are available at many children's hospitals and private clinics. Costs vary but typically include consultation and testing fees. Any confirmed diagnosis and management plan can usually be shared with your NHS GP for ongoing care.