Accuracy of serum IgE concentrations and papule diameter in the diagnosis of cow's milk allergy

Systematic review and meta-analyses on the accuracy of diagnostic tests for IgE-mediated food allergy

The European Academy of Allergy and Clinical Immunology (EAACI) is updating the Guidelines on Food Allergy Diagnosis. We aimed to undertake a systematic review of the literature with meta-analyses to assess the accuracy of diagnostic tests for IgE-mediated food allergy. We searched three databases (Cochrane CENTRAL (Trials), MEDLINE (OVID) and Embase (OVID)) for diagnostic test accuracy studies published between 1 October 2012 and 30 June 2021 according to a previously published protocol (CRD42021259186). We independently screened abstracts, extracted data from full texts and assessed risk of bias with QUADRAS 2 tool in duplicate. Meta-analyses were undertaken for food-test combinations for which three or more studies were available. A total of 149 studies comprising 24,489 patients met the inclusion criteria and they were generally heterogeneous. 60.4% of studies were in children ≤12 years of age, 54.3% were undertaken in Europe, ≥95% were conducted in a specialized paediatric or allergy clinical setting and all included oral food challenge in at least a percentage of enrolled patients, in 21.5% double-blind placebo-controlled food challenges. Skin prick test (SPT) with fresh cow's milk and raw egg had high sensitivity (90% and 94%) for milk and cooked egg allergies. Specific IgE (sIgE) to individual components had high specificity: Ara h 2-sIgE had 92%, Cor a 14-sIgE 95%, Ana o 3-sIgE 94%, casein-sIgE 93%, ovomucoid-sIgE 92/91% for the diagnosis of peanut, hazelnut, cashew, cow's milk and raw/cooked egg allergies, respectively. The basophil activation test (BAT) was highly specific for the diagnosis of peanut (90%) and sesame (93%) allergies. In conclusion, SPT and specific IgE to extracts had high sensitivity whereas specific IgE to components and BAT had high specificity to support the diagnosis of individual food allergies.

[Skin test (Skin Prick Test) in food allergy]

Skin tests, also known as prick tests, in food allergies are restricted to IgE-mediated food allergies, with results that barely indicate sensitization to a certain food and do not necessarily suggest food allergy. The clinical context of the patient is the decisive point before performing any type of food allergy skin test; Contextualizing and relating the patient's clinical picture with the immunological mechanism of IgE-mediated allergies will allow a better selection of the allergy test for each case. Positive tests should be interpreted more carefully, and consider that during early childhood it is common that several patients may have negative specific serum IgE tests in the blood for food allergens compared to those performed on the skin, which are positive. Skin testing can be carried out with standardized strata of foods, but they are not always available for all foods and some are very unstable. Skin tests can even be performed with raw foods, using the prick to prick technique to perform the puncture with fresh foods (especially fruits or vegetables) or other products that are not commercially available. The skin prick test is a test where, after having placed the allergenic extract in drops or with fresh food itself, the puncture must be carried out with a standardized lancet.

Growth and Nutritional Biomarkers in Brazilian Infants with Cow's Milk Allergy at Diagnosis and 18-Month Follow-Up: A Prospective Cohort Study

Purpose

This study aimed to describe the growth, body protein status, and micronutrient biomarkers of Brazilian infants with cow's milk allergy (CMPA) at baseline and at 18 months of follow-up in comparison with their healthy peers.

Methods

Thirty infants with CMPA younger than six months of age were included in this longitudinal study, and their nutritional status was compared with that of 24 non-allergic age-matched children. Anthropometric measurements were used to assess growth, and blood and urine samples were analyzed for protein and micronutrient status. Mixed linear models adjusted for birth weight, socioeconomic status, infant feeding at baseline, weight-for-age, C-reactive protein, serum albumin, micronutrient dietary supplementation, and salt consumption were employed to evaluate the evolution of nutritional parameters throughout the follow-up period.

Results

Overall, the mean age of the children at enrolment was 2.9 (standard deviation 1.7) months, and 29 children (53.7%) were male. Infants with CMPA showed a higher prevalence of functional iron depletion (transferrin saturation <20) (p=0.027), lower serum ferritin (p=0.009), and lower urinary iodine (p=0.034) levels than non-allergic children at baseline. Patients with CMPA showed a higher increment in weight-for-age and length-for-age over time than those in the control group (p<0.01). Mixed linear analyses showed a significantly lower increase in serum vitamin B12 (s-B12) (p=0.001) and urinary iodine (p<0.001) concentrations over time compared to the control group.

Conclusion

Infants with CMPA on a cow's milk elimination diet had a higher weight and length at 18 months of follow-up but showed signs of inadequate iron, iodine, and B-12 vitamin status.

Oral food challenge in children with contact urticaria in reaction to cow's milk

OBJECTIVE

To evaluate the relationship between the occurrence of contact urticaria in reaction to cow's milk in infants and the diagnosis of cow's milk allergy (CMA) established by supervised oral food challenge.

METHODS

In this cross-sectional study, we identified 184 children who had undergone 221 oral food challenge (OFC) at a CMA reference center between July 2015 and August 2019. Of these, 23 (12.5%) had a history of contact urticaria to cow's milk and underwent a total of 30 OFC. Baked cow's milk OFC were excluded, and 21 children were included in the study. All data from clinical history and allergy tests (serum-specific IgE dosages and skin prick test [SPT] with reconstituted cow's milk formula) were recorded on standardized forms. The challenge was conducted with reconstituted cow's milk formula in increasing volumes every 15-20 min.

RESULTS

24 OFC were performed; 13/24 (54.2%) for diagnostic purpose and 11/24 (45.8%) to evaluate cow's milk tolerance. Allergy tests were positive in 14 patients (87.5%). Positive oral challenge outcomes were identified in 7/24. One patient had a late flare of atopic dermatitis and five children presented with immediate urticaria (two generalized urticaria and three perioral urticaria). The median papule diameter was 6.5 mm in patients with a positive OFC and 3.75 mm in the negative group (P = 0.02).

CONCLUSION

The occurrence of contact urticaria might be the only manifestation among infants sensitized to cow's milk with tolerance to oral ingestion. Reactions due to oral challenge were related to a larger wheal diameter on the SPT.

Predictors of a positive oral food challenge to cow's milk in children sensitized to cow's milk

INTRODUCTION AND OBJECTIVES

The diagnosis of IgE-mediated cow's milk allergy (CMA) is often based on clinical history and on specific IgE levels and/or skin-prick tests (SPT), both of which are sensitive but not specific. The gold standard, oral food challenge (OFC), is expensive and time-consuming and involves a risk of severe allergic reactions. This study aimed to determine the value of specific IgEs, ratios of specific IgEs for cow's milk and its components to total IgE, and wheal size on SPT for predicting a positive OFC for CMA.

MATERIAL AND METHODS

We retrospectively studied 72 patients [median age, four years; age range 0.75-15 years] sensitized to cow's milk who underwent OFCs to milk. predictive variables between patients with positive and negative OFCs were compared. Receiver operator characteristic (ROC) curves were uses to assess variables' discriminatory capacity and Youden's index to determine the best cut-offs for predicting CMA.

RESULTS

The OFC was positive in 39 (54%) patients. Wheal size on SPT and all specific IgEs and specific-to-total IgE ratios were significantly different between patients with positive OFCs and those with negative OFCs (p<0.001). The variable with the greatest area under the ROC curve was casein-specific IgE (0.98), followed by β-lactoglobulin-specific IgE (0.923), casein-specific-to-total-IgE ratio (0.919), and α-lactalbumin-specific IgE (0.908). Casein-specific IgE ≥0.95kU/L yielded 88.9% sensitivity and 90.9% specificity.

CONCLUSIONS

In our center, casein-specific IgE >0.95kU/L can obviate an OFC to cow's milk for the diagnosis of CMA in patients sensitized to cow's milk with a compatible history.