Total serum IgE and PhadiatopTM are 2 key tests employed for in-vitro screening of atopy. Acknowledging the possibility of unique allergen prevalences in the Indian subcontinent, aim of the study was to understand the IgE seroprevalence of common food & inhalant allergens, in Indian adult population with suspected atopic disease & compare performance of PhadiatopTM (US version) & Total IgE as screening tests.
Methods:
The study was carried out in an accredited private medical laboratory in Mumbai, India. It involved retrospective data analysis on 545 sera, collected between 2013 & 2014, from patients with suspected allergic disease. Tests included Allergen specific IgE testing for 29 common food and inhalant allergens ( ImmunoCAP, Ms. Thermofischer Phadia, Sweden) .335 sera had also been simultaneously screened using Adult PhadiatopTM (ImmunoCAP, Ms. Thermofischer Phadia, Sweden) ,while 210 were screened for Total IgE (Immulite,Siemens healthcare,USA ).These were designated as Group I & Group II respectively. Both groups had similar age and gender distribution.
Results:
446/545 patients (81.8%) showed sensitization to at least 1 or more allergens. Multisensitization was common and seen in 73.2% sera. Most prevalent allergens were Housedust mite-D pternyssinus (58.5%) ,Cockroach (57.4%) , Housedust mite-D farinae (56.8%), Shrimp(47.7%),House dust(45.13%) , Weed Chenopodium album pollen (44.2%),Candida albicans(41.8%) , Weed Artemisia vulgaris-Mugwort pollen and Wheat (32%).
Using Allergen specific IgE as standard (Cut off of 0.1 kua/l), the sensitivity & specificity of Phadiatop in Group I was 62.1% and 98.4% respectively. Phadiatop sensitivity increased if only Allergen specific IgE values >0.5 kua/l were considered, i.e those more likely to be involved in symptomatic allergic disease. Phadiatop missed cockroach and shrimp positive sera. Though Phadiatop is not intended to screen for food allergies, cross reactivity between certain pollens and foods yielded few positive screening results. The sensitivity & specificity of Total IgE in Group II was 40.8 % and 100% respectively. Total IgE not only missed low level sensitization, but also missed some sera with high positive allergen specific IgE results.
Conclusion:
PhadiatopTM was found to be a satisfactory screening test for atopy and outperformed Serum Total IgE. Looking at the trends in inhalant and food allergen seroprevalence , current study was able to establish a preliminary list of allergens relevant in the Indian context. These could be tested in addition to a Phadiatop or as a follow-on to a negative Phadiatop TM in the event of strong clinical history of allergic disease.