Minimal clinically important difference of the Visual Analogue Scale for allergic rhinitis in Thai patients

Background: The Visual Analogue Scale (VAS) is recommended for assessing allergic rhinitis severity and treatment response. Determination of the minimal clinically important difference (MCID) of the VAS assists physicians in making treatment decisions. Objective: This study aimed to determine the MCID of the VAS in Thai patients with allergic rhinitis. Methods: A prospective study was conducted in adult patients with allergic rhinitis. Participants recorded daily VAS scores for 28 days using a 100-mm scale (0 = not at all bothersome; 100 = most bothersome), and symptom change was evaluated using the Global Rating of Change Scale. MCID was calculated using anchor-based and distribution-based methods. The anchor-based estimate was determined as the primary value for interpretation because it directly reflects patient-perceived change. Results: A total of 316 patients were analyzed. Mean VAS scores decreased throughout the treatment period. The anchor-based MCID of VAS was 43.86 ± 27.49, whereas the distribution-based MCID was 32.25 mm. The mean VAS change reached the MCID threshold on day 5 after treatment. Conclusion: The MCID of the VAS for Thai patients with allergic rhinitis was 43.86 mm. Clinically meaningful improvement is generally perceived after 5 days of treatment, suggesting that this is an optimal follow-up time.