# Basophil Activation Test as Biomarker of Severity and Threshold of Allergic Reactions to Cow's Milk During Oral Food Challenges

## TL;DR

This study shows that the basophil activation test can predict severe allergic reactions and low reaction thresholds in children with cow's milk allergy.

## Contribution

The study identifies the basophil activation test as a novel biomarker for predicting severity and reaction thresholds in cow's milk allergy.

## Key findings

- The basophil activation test (BAT) was the only biomarker that could distinguish severity and threshold groups in cow's milk allergy.
- BAT had 71% sensitivity and 100% specificity for identifying severe reactors to baked milk.
- The threshold of reactivity during fresh milk challenges was 70% lower than that of baked milk challenges.

## Abstract

Cow's milk allergy is the most common food allergy worldwide and the top cause of food anaphylaxis fatalities. Identifying patients at higher risk of severe symptoms as well as patients with a lower threshold of reactivity would improve their management. We aimed to assess the utility of putative biomarkers to identify these high‐risk patients.

The severity of allergic reactions to baked milk (BM) and to fresh milk (FM) during oral food challenges (OFC) was assessed prospectively during the BAT2 study (NCT03309488), according to the Practall guidelines. Demographic, clinical and immunological parameters were compared between severe/non‐severe and higher/lower threshold reactors to BM or FM. Receiver Operating Characteristic curve analyses were performed to measure the accuracy of biomarkers with discriminative ability.

Seventy‐one children reacted to cow's milk: 22 (15%) to BM and 49 (43%) to FM. Seven (32%) and 12 (24%) reactors had severe symptoms during OFC to BM and FM, respectively. The median cumulative dose of milk protein tolerated was 0.44 g for BM and 0.143 g for FM. The basophil activation test (BAT) was the only biomarker that could distinguish severity and threshold groups. BAT optimal cut‐offs had 71% sensitivity and 100% specificity to identify severe reactors to BM and 96% sensitivity and 41% specificity to identify children reacting to 0.143 g or less of FM.

BAT was the only biomarker for severity and threshold of allergic reactions to BM and FM, respectively. Once applied to clinical practice, BAT can help risk‐stratify cow's milk allergic patients and improve their management.

The threshold of reactivity during fresh milk challenges was 70% lower than that of baked milk challenges, reflecting the higher allergenicity of fresh milk. BAT was the only biomarker statistically significantly different between severity and threshold groups, for baked milk and fresh milk allergies, respectively. Using optimal cut‐offs, sensitivity and specificity of BAT for severity of reactions to baked milk were 71/100% and for threshold of reactivity to fresh milk were 96%/41%. BAT, basophil activation test; IgE, immunoglobulin E; OFC, oral food challenge; SPT, skin prick test.