Asthma as a Type I Hypersensitivity Reaction and Laboratory Diagnosis: A Review of Current Literature

Asthma is a common chronic respiratory disease affecting people worldwide. Globally, over 260 million people were estimated to have asthma in 2019, with an incidence peak in children aged 5–9 years. Prevalence tends to be higher in high-income countries (~6–8%) than in low- and middle-income countries (~2–5%). In Nigeria, national surveys find that 2.5% of people report doctor-diagnosed asthma, while 6.4% have “clinical asthma” (symptoms suggestive of asthma) and 9.0% report wheezing in the past year. Rates rise with age: e.g. 10–17-year-olds have clinical asthma in ~3–10%. In Southeast Nigeria (Enugu State), school-based studies similarly show high prevalence: one recent survey found overall bronchial asthma in ~11.3% of children, with urban pupils (13.1%) slightly more affected than rural (11.2%). Asthma is an IgE‐mediated type I hypersensitivity reaction characterized by an initial sensitization to inhaled allergens, followed by allergen challenge that triggers mast cell and basophil degranulation, resulting in bronchoconstriction, mucus hypersecretion, and airway inflammation. Understanding asthma immunopathology is essential for precision therapy. Therefore, a central objective is to precisely phenotype patients so that appropriate biologics can be selected. Standardized biomarkers are critical for this. For instance, serum total and specific IgE (or skin prick) assess atopy, blood eosinophil count and sputum eosinophils measure airway eosinophilia, and FeNO reflects IL-13–driven inflammation. International guidelines endorse such testing: NICE and ATS recommend FeNO for asthma diagnosis and monitoring, and ERS/ATS guidelines highlight sputum eosinophil counts and FeNO to guide therapy in severe casest. In practice, an elevated FeNO (>50 ppb) or blood eosinophils (≥150–300 cells/µL) suggests Type-2-high asthma responsive to steroids and biologics. Indeed, sputum-guided management (treating to maintain eosinophils <3%) reduces exacerbations, although its use is currently limited to specialty centres.