Minimal clinically important difference for the rhinoconjunctivitis quality of life questionnaire in allergic rhinitis in Thai population

BACKGROUND: Clinical measurement of the severity of allergic rhinitis (AR) can be assessed by symptoms score and patient quality of life (QoL). The magnitude of change in both symptoms and patient QoL should be considered in the management of AR. OBJECTIVE: The aim of this study was to determine the minimal clinically important difference (MCID) in AR in Thai population. METHODS: This prospective study recruited AR patients that attended our clinic during September 2011 to February 2012. The Rhinoconjunctivitis Quality of Life (Rcq-36) questionnaire was used to evaluate patient QoL. The Global Rating of Change Scale (GRCS) was used to assess improvement or deterioration in condition. The MCID was determined using an anchor-based method based on the GRCS, which was compared to the MCID determined by a distribution-based method based on the standard deviation (SD). RESULTS: Three hundred seventy-two patients with chronic rhinitis were recruited. Eighty-four of those had positive skin prick test and be diagnosed as AR. Of those, 79 completed the study and were included in the final analysis. A change of 2 points on the GRCS yielded an MCID for overall QoL of 0.21 ± 0.57. When applying the distribution-based method, an SD of 1.5 SD yielded an MCID for QoL of 0.27. For the rhinitis symptoms domain, the MCID was 0.42 ± 0.72. CONCLUSIONS: The MCID for overall QoL and rhinitis symptoms in Thai AR patients was found to be 0.21 ± 0.57 and 0.42 ± 0.72, respectively. MCID can be applied for determining the clinical significance of treatment efficacy in AR.