Appropriate Skin Prick Tests Can Limit Risk of Oral Food Challenges in Pediatric Allergies

Kok Wee Chong, MBBS, MRCPCH

Credit: LinkedIn

A study conducted in Singapore has helped to elucidate the sensitivity and specificity of skin prick test (SPT) and food-specific IgE values and how these can work in concert with oral food challenges (OFC) to help diagnose food allergies in children in a safe manner.¹

“An OFC is an essential tool in the diagnosis of food allergy but is time and resource consuming, carrying with it risks of reactions. Decision points using 95% positive predictive value (PPV) of SPT and food-specific IgE values can aid clinicians in the risk stratification of OFCs,” Kok Wee Chong, MBBS, MRCPCH, Allergy Service, Department of Pediatrics, KK Women's and Children's Hospital, Singapore, and Pediatrics Academic Clinical Program, SingHealth Duke-NUS Academic Medical Centre, Singapore, and colleagues wrote.¹ “The diagnostic accuracies of these tests vary between the different food and patient population tested. We lack reliable decision points to be used in our Singapore population, especially since PPV is highly dependent on the prevalence of disease.”

Chong and colleagues examined the diagnostic accuracies of SPT and sIgE in children who had undergone an open OFC to peanut, egg, cow's milk or wheat using a 5-year retrospective chart review. They analyzed a total of 740 OFCs toward peanut (n = 73/304 positive), cooked hen's egg (n = 25/263 positive), cow's milk (n = 12/99 positive) and wheat (n = 41/74 positive). Positive SPTs (≥ 3 mm) for peanut, egg and cow's milk generally yielded high sensitivity/negative PV (NPV) but low specificity/PPV. A positive egg or milk-sIgE (≥ 0.35 kUA/L) provided 100% sensitivity and NPV, with low specificity and PPV.¹

The findings can help perform better risk stratification, as the data suggest that children with high sensitivity/NPV may have safe, at-home OFCs, while OFCs are unnecessary in those with high specificity/ PPV that suggests a persistent food allergy, and may reduce the need for OFCs, particularly risky OFCs.

Notably, a positive Ara h 2-sIgE (≥ 0.35 kUA/L) provided high specificity of 92%, which is consistent with previous reports of it being the single most important predictor of peanut allergy.^1,2 The investigators also found that the impact of individual tests was limited, as , receiver operating characteristic (ROC) curves all modalities show poor diagnostic performance (area under the curve < 0.8) on SPT across all 4 foods except egg, especially for milk and wheat. Positive likelihood ratios (LRs) on diagnostic readouts also rarely reached over 10 or under 0.1 for negative LRs.¹

The threshold with 95% PPV was achieved for SPT at a cut-off of 12.5 mm (peanut), 11.0 mm (egg) and 6.0 mm (wheat). Thresholds with 95% PPV were 2.95 kUA/L for Ara h 2-sIgE and 2.25 kUA/L for ω-5 gliadin-sIgE.¹

“In conclusion, findings of this study are helpful in informing clinical practice in the care of children with food allergy in Singapore, allowing for better risk stratification in OFCs. Future research should focus on predictive modelling using clinical parameters, biomarkers in conjunction with SPTs and sIgE, to improve diagnostic accuracy of these tools,” Chong and colleagues concluded.¹

REFERENCES

1. Chong KW, Sultana R, Lee MP, et al. Diagnostic Accuracy of Skin Prick Test, Food-Specific IgE and Component Testing for IgE-Mediated Peanut, Egg, Milk and Wheat Allergy. Clin Exp Allergy. Published online October 7, 2024. doi:10.1111/cea.14578

2. R. X. Foong, J. A. Dantzer, R. A. Wood, and A. F. Santos, “Improving Diagnostic Accuracy in Food Allergy,” J Allergy Clin Immunol 9, no. 1 (2021): 71–80, https://doi.org/10.1016/j.jaip.2020.09.037.