Minimum number and types of allergens for a skin prick test panel in Thai children with allergic respiratory diseases

Identification of allergen sensitization in each country is necessary to provide comprehensive knowledge of locally prevalent allergen sensitization, which should be helpful in personalized education in allergen avoidance and management of an allergic disease. In addition, determining the minimum number and types of allergens needed to test is a cost-effective approach. However, the prevalence of allergen sensitization in Thai children has not been studied.

In the present study, we identified eight allergens (Dermatophagoides pteronyssinus, Dermatophagoides farinae, German cockroach, American cockroach, cat, Acacia, Bermuda grass, and careless weed) that were sufficient to identify 99–100% of sensitized children under 18 years of age with symptoms suggestive of allergic rhinitis or asthma or both. Our results were consistent with previous studies that found only eight to nine allergens were sufficient to identify allergen sensitization in children [16,17,18]. However, the types of allergens were different in different countries and geographies [19].

Sahiner et al. reported that the most common allergen sources in Turkey were grass, followed by house dust mite, cat, weeds, and Alternaria species. Testing with nine allergen extracts (Festuca pratensis, Dermatophagoides pteronyssinus, Phleum pratense, Alternaria alternata, cat, Lolium perenne, Dermatophagoides farinae, Cynodon dactylon, and cockroach) identified approximately 95% of allergen sensitization in Turkish children under 18 years old with suspected respiratory allergy [17]. These results differed from our results. We showed that the three most common causes of allergen sensitization in Thai patients were indoor allergens, which were house dust mite followed by cockroach and cat. Grass and pollen had lower sensitizations than indoor allergens. Only three allergen extracts, which included Dermatophagoides pteronyssinus, Dermatophagoides farinae, and German cockroach, were adequate to identify at least 95% of all sensitized children under 18 years of age. If we increased the number of extracts to eight to include Acacia, cat, American cockroach, Bermuda grass, and careless weed, sensitization was detected in 99–100% of the cases.

Wang et al., who performed SPTs in China, included children and adults with allergic rhinitis. They found that the predominant aeroallergen was dust mite with a sensitization rate of over 90% in the whole group, while other allergens, such as pollen, mold, and cockroach, affected less than 10%. Their results were similar to the prevalence results of our study. We reported house dust mite as the most common sensitization (approximately 85%), while other allergens, such as pollen, mold, and cockroach, affected less than 10% in sensitized children. However, the selection of allergens in the panel by Wang et al. was different. In a panel of three allergens, they used Dermatophagoides farinae, Dermatophagoides pteronyssinus, and Platanus, which provided a positive sensitization rate > 95%. In a panel of eight allergens, they used Dermatophagoides pteronyssinus, Dermatophagoides farinae, Platanus, Artemisia, Cryptomeria, Blattella germanica, Humulus, and Alternaria, which was sufficient to identify over 99% of sensitized patients suffering from allergic rhinitis symptoms in Central China [18].

A recent study from Jordan reported only eight allergen extracts were necessary to identify 95% of the sensitized patients. The eight allergen extracts used in children with allergic rhinitis or asthma or both were olive pollen, Dermatophagoides pteronyssinus, Salsola kali, cereals, wall pellitory, Dermatophagoides farinae, cypress, and Alternaria [16].

In this current study, the number and types of allergens in the minimum test panel differed slightly among age groups, which was consistent with other studies [17, 20]. However, the optimized panel of eight allergens for Thai children was able to identify 99–100% of sensitized children.

The house dust mite was the most common sensitization, followed by cockroach and cat. The other allergens including pollen, weed, dog dander, and mold affected less than 5% in these children. Indoor allergens are common in Thai children, which is consistent with previous studies in Thailand [14, 21, 22].

The eight allergens selected for this study were optimized for Thai subjects in clinical practice. The panel of three allergens (Dermatophagoides pteronyssinus, Dermatophagoides farinae, and German cockroach) can be used for the initial screening in areas with limited budgets. The results of this study suggest using the additional five extracts (Acacia, cat, American cockroach, Bermuda grass, and careless weed) for Thai children who tested negative in the initial screening, which was only about 5% of children in the initial screening in this study. However, the patterns of allergen sensitization are unique in each country. Therefore, physicians in each country or geographical region need to establish the optimal number and types of allergens for screening.

The strength of this study is that this is the first study to determine the minimal number and type of allergen extracts for a SPT panel to detect allergen sensitization in Thai children with allergic respiratory disease. This study demonstrated that only eight allergens were appropriate for detection in sensitized children. It reduces the number of test allergens used in current practice, which can also reduce both costs and physician workload, not to mention the discomfort of the needle prick in children.

The limitations in this study need to be stated. First, we focused only on sensitization and did not explore the clinical relevance of sensitization and symptoms. However, the retrospective chart review limited our ability to gather data on the clinical relevance. A future prospective study would be helpful. Second, our study aimed to identify the minimal number of allergens in the SPT panel to achieve the highest positive rate; therefore, some allergens were not included (e.g. dog). If patients report clinical relevance to an allergy, they should be tested. Finally, a cost effectiveness analysis was not performed, which requires further study.

In summary, indoor allergens (dust mites, cockroaches, and cats) were common causes of sensitization. Our study showed that the eight extracts of Dermatophagoides pteronyssinus, Dermatophagoides farinae, German cockroach, Acacia, cat, American cockroach, Bermuda grass, and careless weed were the optimal allergens for the SPT in Thai children with allergic rhinitis or asthma.

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