Ara h 2 sIgE tests preferred for assessing peanut allergies in children
MedWire News: Findings from the HealthNuts study in Australia indicate that the Ara h 2-specific immunoglubulin (sIg)-E diagnostic tool is more accurate in detecting peanut allergies than either a skin prick test (SPT) or a blood test for peanut-specific IgE.
Several allergens in peanuts have been identified, with Ara h 2 being the principal allergen (found in 90% to 100% of those with peanut allergies). Earlier study results have indicated that tests for Ara h 2 sIgE may have higher specificity and sensitivity than other peanut allergy tests, note Katrina Allen (Royal Children's Hospital, Parkville, Australia) and colleagues.
Indeed, both SPTs and peanut-specific IgE have low specificity and high sensitivity for peanut allergy, leading to low positive predictive value (PPV).
The researchers explain that allergy tests are more useful when they have a PPV of 95% or higher. Below this level, it is unclear whether a positive result is a true clinical allergy, and more expensive, time-consuming oral food challenges (OFCs) therefore have to be administered to definitively determine the presence of a peanut allergy.
The HealthNuts study was designed to determine if Ara h 2 sIgE measurement could accurately predict peanut allergy in a population-based setting. Infants who were aged 11 to 15 months, recruited through local immunization sessions, first had SPTs done for peanuts and other foods. Out of this group, 100 infants with positive peanut SPTs and 100 negative controls were given a peanut oral food challenge (OFC). Levels of whole peanut sIgE and Ara h 2 sIgE were assessed in all of them.
As reported in the Journal of Allergy and Clinical Immunology, using an equivalent specificity of 98%, the Ara h 2 sIgE sensitivity was 60%, indicating that the test correctly identified 60% of infants with confirmed peanut allergy. The corresponding sensitivity of the whole peanut sIgE test was 26%. Using a combination of both measurements was predicted to reduce the total number of OFCs required from 47.5% to 16%.
The investigators note that this was the first study to review the predictability of the Ara h 2 sIgE in a population-based setting.
They recognize that the results may not necessarily be the same in older children. However, since peanut allergy testing is already common in children aged 1 year and younger, they feel that "Ara h 2 sIgE testing will provide a method of screening for peanut allergy that reduces the need for OFCs," and could potentially supplement or replace measurement of whole peanut sIgE.
By Stephanie Leveene