EVIDENCE-BASED ANSWER
A WELL-DESIGNED ORAL FOOD CHALLENGE (OFC) is the most reliable diagnostic test for infants whose clinical history and physical examination suggest a specific food allergy (strength of recommendation [SOR]: C, consensus guidelines).
Serum-specific immunoglobulin E (IgE), atopy patch testing (APT), and skin prick testing (SPT) are all alternatives to OFC, but the likelihood ratios are not robust and the tests vary widely in sensitivity and specificity to different allergens. For diagnosing egg and milk allergies, larger wheal sizes with SPT are more predictive of a positive OFC (SOR: C, extrapolated from cohort studies evaluating mixed populations of infants, children, and teenagers).
Evidence summary
The American Academy of Allergy, Asthma and Immunology (AAAAI) states that a double-blind, placebo-controlled OFC is the best test for diagnosing infants clinically suspected of having food allergies (that is, who develop gastrointestinal symptoms after eating a specific food). However, performing an OFC in an infant is often difficult and potentially dangerous, especially if a severe allergy is suspected; testing also may eliminate nutritious foods, such as milk and eggs, from the infant’s diet.1 For these reasons, physicians have sought simpler alternatives to the OFC.
Comparisons of serum and skin testing with OFCs produce variable, weak results
Two large cohort studies compared OFCs with serum and skin testing in infants, children, and teenagers. Overall, serum and skin testing didn’t produce robust results and the results varied with the antigen (TABLE).
TABLE
How allergy tests in infants and children compare with an oral food challenge
| Test* | Sensitivity (%) | Specificity (%) | LR+ | LR- |
|---|---|---|---|---|
| Milk | ||||
| IgE2 | 83 | 53 | 1.8 | 0.32 |
| SPT3 | 85 | 70 | 2.8 | 0.21 |
| APT3 | 31 | 95 | 6.2 | 0.73 |
| Egg | ||||
| IgE2 | 97 | 51 | 2.0 | 0.59 |
| SPT3 | 93 | 54 | 2.0 | 0.13 |
| APT3 | 41 | 87 | 3.2 | 0.68 |
| Wheat | ||||
| IgE2 | 79 | 38 | 1.3 | 0.55 |
| SPT3 | 75 | 64 | 2.1 | 0.39 |
| APT3 | 27 | 89 | 2.5 | 0.82 |
| Soy | ||||
| IgE2 | 69 | 50 | 1.4 | 0.31 |
| SPT3 | 29 | 85 | 1.9 | 0.84 |
| APT3 | 23 | 86 | 1.6 | 0.90 |
| APT, atopy patch test; IgE, serum immunoglobulin E; LR+, positive likelihood ratio; LR–, negative likelihood ratio; SPT, skin prick test. *Positive tests were defined as follows: IgE=serum level >0.35 kU/L (detection limit of assay). SPT=wheal ≥3 mm. APT=erythema with skin surface change. | ||||
In 1 study, researchers compared specific serum IgE levels with OFC results for 4 foods—milk, eggs, wheat, and soy—in 501 consecutive pediatric patients referred to an allergy ward based on clinical or parental suspicion of food allergy. Children ranged in age from 1 month to 16 years (median age 13 months); results for infants were not provided separately. Eighty-eight percent of the children were atopic. Investigators measured serum IgE (using the Pharmacia CAP-system fluorescence enzyme immunoassay) before administering the OFCs.