Secretoglobin Felis Domesticus 1 (Fel d 1) specific immunoglobulin E in diagnosis of patients with respiratory allergy to cats.

Cat allergy is a common cause of respiratory allergic diseases, such as asthma and allergic rhinitis. Secretoglobin Felis domesticus 1 (Fel d 1) is the major cat allergen, widely distributed in the environment and difficult to avoid. Measuring Fel d 1-specific Immunoglobulin E (sIgE) provides an important diagnostic approach for evaluating sensitisation and disease severity. The present study assessed the diagnostic value of allergen-specific IgE to secretoglobin Fel d 1 in Egyptian adult patients with respiratory allergy sensitised to cats. This cross-sectional study included 35 patients with clinical diagnoses of asthma and/or allergic rhinitis, all positive for cat dander by skin prick test (SPT). Complete blood count, total IgE, and serum Fel d 1-sIgE (measured using ImmunoCAP) were performed. Of the 35 patients, 40% tested positive for Fel d 1-sIgE. Positive Fel d1 -sIgE was significantly associated with older age, history of cat exposure, and family history of allergy (p < 0.05). Patients with positive Fel d 1-sIgE levels showed significantly higher total IgE, leukocyte, and eosinophil counts. Fel d 1-sIgE levels were positively correlated with asthma and allergic rhinitis severity. ImmunoCAP Fel d 1-sIgE testing accurately differentiates true cat allergy from cross-sensitization. This study represents one of the first regional data utilizing this method in an Egyptian cohort, enhancing diagnostic precision, assessing disease severity, and supporting personalized treatment strategies.