Development and validation of the Food Allergy Quality of Life Questionnaire - Adult Form

Background: Health-related quality of life (HRQL) may be affected by food allergy. Presently, no disease-specific HRQL questionnaire exists for food allergic adults. Therefore, we developed and validated the Food Allergy Quality of Life Questionnaire - Adult Form (FAQLQ-AF) in the Dutch language. Methods: Twenty-two food allergic patients (>= 18 years) were interviewed and generated 180 HRQL items. The most important items were identified by 54 food allergic patients using the clinical impact method resulting in the FAQLQ-AF containing 29 items (score range 1 'not troubled' to 7 'extremely troubled'). The FAQLQ-AF, the Food Allergy Independent Measure (FAIM) and a generic HRQL questionnaire (RAND-36) were sent to 100 other food allergic adults for cross-sectional validation of the FAQLQ-AF. Results: Cross-sectional validity was assessed by the correlation between FAQLQ-AF and FAIM (rho = 0.76, P < 0.001). The FAQLQ-AF had excellent internal consistency (Cronbach's alpha = 0.97). The FAQLQ-AF discriminated between patients who differ in severity of symptoms (anaphylaxis vs no anaphylaxis, total FAQLQ-AF score 4.9 vs 4.1; P = 0.041) and number of food allergies (> 3 food allergies vs <= 3 food allergies, total FAQLQ-AF score 5.2 vs 4.2; P = 0.008). The total FAQLQ-AF score was correlated with one RAND-36 scale (convergent/discriminant validity). Conclusions: The FAQLQ-AF is the first disease-specific HRQL questionnaire for food allergic adults and reflects the most important issues that food allergic patients have to face. The questionnaire is valid, reliable and discriminates between patients with different disease characteristics. The FAQLQ-AF is short and easy to use and may therefore be a useful tool in clinical research.