BACKGROUND: Allergic asthma is a chronic respiratory condition characterized by inflammation and constriction of the airways in response to specific allergens. This study aimed to assess serum and biopsy biomarkers to predict the severity of allergic asthma. METHODS: A total of 18 allergic asthma patients and 15 healthy controls (HCs) were included from April to August 2021 in Par hospital, Erbil-Iraq. The blood and bronchial biopsy were taken, the serum biopsy marker were assessed via ELISA and immunohistochemistry (IHC) methods. RESULTS: It was showed no significant difference in age between allergic asthma patients and HCs (P= 0.285), although patients with allergic asthma had a significantly higher BMI (P= 0.028). Allergic asthma patients exhibited significantly elevated levels of serum eosinophil cationic protein (ECP), fibroblast growth factor 23 (FGF-23), and fibroblast growth factor 18 (FGF-18) compared to HCs (P<
0.0001). IHC analysis revealed significantly higher levels of myeloperoxidase (MPO) positive cells, activated eosinophils (EG2) positive cells, mast cells, FGF-18 positive cells, and FGF-23 positive cells in bronchial biopsy samples from allergic asthma patients compared to HCs (P<
0.0001). Additionally, serum FGF-18, EG2 positive cells, and FGF-18 positive cells were negatively correlated with lung function (FEV1/FVC), while asthma score showed a significant positive correlation with these markers. CONCLUSION: Serum FGF-18, EG2 positive cells, and FGF-18 positive cells are promising biomarkers that can predict improvements in the FEV1/FVC ratio and reductions in asthma score, highlighting their potential utility in assessing the severity of allergic asthma and guiding treatment decisions.