Specific IgE Testing

Specific IgE (sIgE) testing is a blood test that measures IgE antibodies against one named allergen, such as egg, peanut, cow’s milk, House Dust Mites or Pollen. The usual laboratory method is ImmunoCAP, which replaced the older RAST. It answers the same question as Skin Prick Testing: is the child sensitised? It does not show whether the child will react. For toddlers it has practical advantages. It needs one blood draw rather than patches of clear skin, which children with widespread eczema may lack, and antihistamines do not have to be stopped. The JAAD International review (2022) notes that sIgE is less sensitive than SPT, but it gives allergen- and age-specific cut-offs that help estimate how likely a positive is to be real.

Specific IgE Testing [relates] Skin Prick Testing

Why it misleads in eczema. Children with Atopic Dermatitis often have high total IgE and many “positive” results to foods they eat without trouble. Up to 53% of children with AD have a positive food sIgE or SPT, but only up to 15% react on an Oral Food Challenge (JAAD Int 2022). Negative predictive value is high (>95%), while positive predictive value is only about 40–60% (Healio). The NIAID expert panel (Togias, 2017) says peanut sIgE below 0.35 kUA/L makes peanut allergy very unlikely, but a value of 0.35 or above “lacks adequate positive predictive value”, and such an infant should be referred to a specialist rather than told to avoid peanut. Reporting results as “class 2” or “class 3” is not clinically helpful (JAAD Int 2022). Türe Avcı et al. (2026) add that positive results “do not necessarily indicate clinically relevant allergy”, and that most early food allergy is transient.

Specific IgE Testing [relates] Food Allergy Oral Food Challenge [defines] Food Allergy

When it should and should not be ordered. The AAAAI’s Choosing Wisely advice is that IgE testing (skin or blood) should be guided by the child’s history and examination. Broad food panels without a matching history are discouraged because false positives lead to unnecessary avoidance. That avoidance raises cost and anxiety, and it can cause true allergy by removing tolerated foods (Elimination Diets). NICE CG57 asks clinicians to consider food allergy only after an immediate reaction to a food, or in a baby or young child with moderate–severe eczema that is not controlled despite optimum treatment, especially with gut symptoms or faltering growth. Commercial IgG Food Testing is a different test and is not valid for diagnosing allergy or eczema triggers.

Specific IgE Testing [causes] Elimination Diets Choosing Wisely [regulates] Specific IgE Testing NICE CG57 [regulates] Specific IgE Testing

Other uses relevant to toddlers. In the LEAP Trial, peanut sIgE was tracked alongside SPT. Avoidance-group children more often developed high peanut sIgE, and the main allergy diagnosis still relied on challenge. sIgE to individual nut proteins (component-resolved diagnostics) can help separate primary Tree Nut Allergy from pollen cross-reactivity (Nutrients 2024). Treatment can also change results: in children with AD, Dupilumab lowered nut sIgE by roughly 70–82% (Nutrients 2024). So a falling number does not by itself show that a child has outgrown an allergy.

LEAP Trial [relates] Specific IgE Testing Dupilumab [relates] Specific IgE Testing

Connections

• Skin Prick Testing — blood equivalent; same low PPV in AD, source: Togias 2017
• Oral Food Challenge — sIgE ≥0.35 kUA/L warrants specialist review/challenge, source: NIAID 2017
• Food Allergy — sensitisation is not allergy; up to 53% positive vs ≤15% challenge-proven, source: JAAD Int 2022
• Elimination Diets — false positives drive unnecessary avoidance, source: JAAD Int 2022
• Choosing Wisely — test only when guided by history, source: AAAAI 2012
• NICE CG57 — when to consider food allergy testing, source: NICE CG57
• IgG Food Testing — not a valid alternative, source: AAAAI Choosing Wisely
• Tree Nut Allergy — component sIgE separates primary allergy from pollen cross-reactivity, source: Nutrients 2024
• Dupilumab — lowers nut sIgE ~70–82% in paediatric AD, source: Nutrients 2024