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Optimal wheal size, IgE cutoff for peanut allergy risk assessment in SG kids

Jairia Dela Cruz
19 Aug 2019

A peanut skin prick test (SPT) wheal size of ≥8 mm or a peanut-specific immunoglobulin E (IgE) of ≥6 kU/L strongly predicts clinical reaction to peanut ingestion in children, as shown in a local study.

“This is the first study examining the diagnostic performance of SPT and peanut-specific serum IgE concentrations in predicting clinical reactions to peanut ingestion in peanut sensitized children in Singapore,” according to the investigators. “The cutoff values derived in this study can help clinicians in the risk assessment of oral food challenge (OFC).”

The investigators reviewed the medical records of 654 patients with a positive SPT to peanut, among whom 251 had no known peanut exposure, to identify clinically useful decision points to be used for risk stratification of OFC. The final sample size comprised 269 patients with a clinical diagnosis of peanut allergy based on recent immediate reaction to peanut (PA group; mean age, 3.9 years; 53.9 percent male) and 59 who were tolerant (PT group; mean age, 3.7 years; 62.7 percent male).

Atopic diseases, especially atopic dermatitis, were highly prevalent in both groups. However, significantly more patients in the PA than in the PT group had rhinitis as a comorbidity (adjusted odds ratio, 2.39, 95 percent CI, 1.30–4.38; p=0.0050).

A wheal size of ≥8 mm and a peanut-specific IgE of ≥6 kU/L independently showed good diagnostic performance, each yielding a positive predictive value (PPV) of >95 percent for peanut allergy. When combined, the PPV increased to 100 percent. [Asia Pac Allergy 2019;9:e21]

Results for area under curve, according to the receiver operating characteristic analysis, were generally better for SPT than for peanut-specific IgE. Of note, the larger the wheal size on SPT, the higher the probability of a clinical reaction to peanuts.

However, the investigators noted that while the wheal size cutoff of ≥8 mm had high specificity (86.4 percent), sensitivity was relatively low (61.7 percent). “Thus, in the context of a relevant clinical history, the SPT may be used to confirm a diagnosis of a peanut allergy but not to be used to rule out a diagnosis of peanut allergy.”

While the finding for SPT agrees with other studies, the peanut-specific IgE identified presently appears to be lower than that previously reported. [J Allergy Clin Immunol 2006;117:1506-1508; J Allergy Clin Immunol 2013;132:874-880; Clin Exp Allergy 2017;47:719-739; J Allergy Clin Immunol 2005;115:1291-1296]

“[The disparity] could be explained by the fact that our study's diagnosis of peanut allergy was only based on clinical history of an allergic reaction, whereas the other studies quoted used OFCs (open or blinded) as the outcome,” the investigators said. “Selection bias may also account for this difference as the attending allergists were more likely to advise strict peanut avoidance if the peanut-specific IgE was high, resulting in a much smaller number of peanut tolerant patients compared to peanut sensitized patients.”

Finally, the peanut-specific IgE threshold might truly be lower in Singaporean children than in international cohorts, they added.

As the present study did not establish the diagnosis of peanut allergy using the gold standard of a double-blind, placebo-controlled food challenge, the investigators called for additional work to confirm the diagnostic performance of skin prick and peanut-specific IgE testing in predicting OFC outcomes, as well as to better determine the clinical decision points for children in the Asia-Pacific region.

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