Agreement Between Predictive, Allergen-Specific IgE Values Assessed by ImmunoCAP and IMMULITE 2000 3gAllergy™ Assay Systems for Milk and Wheat Allergies

概要

Introduction
The ImmunoCAP specific IgE (ImmunoCAP) and the IMMULITER2000 3gAllergy™ (3gAllergy) systems are major quantitative allergen・specific IgE (slgE) assay methods. Due to the heterogeneous nature of the allergenic extracts and differences in the assay format, quantitation of allergen・slgEs is not expected to correlate well between the methods.

Background
In regular clinical practice with access to different assay systems, a clinician may receive discordant reports from laboratories that employ various systems, and interpretation of the "different" data is difficult. It would be ideal that the slgE assays could be harmonized to give compatible results.

Objectives
This study aimed to determine and correlate the predictive values of slgE by both systems in diagnosis of milk & wheat allergies.

Methods
This was a prospective observational multicenter study. Oral food challenges (OFCs) were performed to all enrolled patients to diagnose -either true allergy in a 1 year old group (A) or tolerance in a 2-6 year old group (B). The challenge food was divided into graded doses and objective clinical reactions were observed and we measured levels of slgE to milk, casein and beta-lactoglobulin (BLG) in milk group and wheat and omega5 gliadin (OM5G) slgE in the wheat group by both methods. Receiver operator characteristic (ROC) analysis was used to determine the area under the curve (AUC). Logistic regression analysis was performed to obtain the positive prediction rate for each measured value and generate probability curves.

Results
Milk and wheat OFCs were performed for 87 and 102 Group A patients, and 124 and 82 Group B patients, respectively. ImmunoCAP and 3gAllergy showed similar AUCs in both groups for milk and wheat allergy, with a few differences (0.7-0.9). 3gAllergy demonstrated slightly higher AUCs in milk allergy and OM5G・slgE than ImmunoCAP while ImmunoCAP showed slightly higher AU Cs than 3gAllergy for wheat・slgE. Overall, all・the curves with the two tests for milk OFC and wheat OFC were very similar in shape, indicating comparable diagnostic performance with the assays. Using Pearson's coefficient, logarithmically converted and compared specific IgE antibody titers of milk and wheat were very well correlated, as well as the positive prediction rates of each test for the same serum (R>0.9).

Consideration
The results of the comparison of the 2 measurement methods, ImmunoCAP and 3g Allergy for milk and wheat, showed a strong correlation in log-transformed values and predicted probabilities between both methods, thus signifying the comparability of their results. To facilitate the comparison, physicians can use a conversion table createcl from the graph obtained by logarithmically converting the measured values from both methods.

Conclusion
The 2 major systems to measure allergen゜specificIgE, ImmunoCAP and 3gAllergy, may be interchangeable for diagnosis of milk and wheat allergies in young children.