Visual analogue scale (VAS) as a monitoring tool for daily changes in asthma symptoms in adolescents: a prospective study

BACKGROUND Success in asthma management hinges on patients' competency to detect and respond to ever-changing symptom severity. Thus, it is crucial to have reliable, simple, and sustainable methods of symptom monitoring that can be readily incorporated into daily life. Although visual analogue scale (VAS) has been considered as a simple symptom assessment method, its utility as a daily symptom monitoring tool in adolescents is unknown. This study was to determine the concurrent validity of VAS in capturing diurnal changes in symptoms and to examine the relationships between VAS and asthma control and pulmonary function. METHODS Forty-two adolescents (12-17 years old) with asthma completed daily assessment of symptoms twice per day, morning and bedtime, for a week using VAS and 6-item symptom diary concurrently. Asthma control was measured at enrollment and 6 month later, and spirometry was conducted at enrollment. Pearson correlations, multilevel modeling and regression were conducted to assess the relationships between VAS and symptom diary, asthma control and FEV1. RESULTS Morning and evening VAS was positively associated with symptom diary items of each corresponding time frame of the day (r = 0.41-0.58, p < 0.0001). Morning VAS was significantly predicted by morning diary data reflecting nocturnal wakening (β = 2.13, p = 0.033) and morning symptoms (β = 4.09, p = 0.002), accounting for 57% of the total variance of morning VAS. Similarly, changes in four evening diary items, particularly shortness of breath (β = 2.60, p = 0.028), significantly predicted changes in evening VAS, accounting for 55% of the total variance. Average VAS scores correlated with asthma control (r = 0.65, p < 0.001) and FEV1 (r = -0.38, p = 0.029), and were predictive of asthma control 6 months later (β = 0.085, p = 0.006). CONCLUSIONS VAS is a valid tool capturing diurnal changes in symptoms reflected in a multi-item symptom diary. Moreover, VAS is a valid measure predicting concurrent and future asthma control. The findings suggest VAS can be a simple alternative to daily dairies for daily symptom monitoring, which can provide invaluable information about current and future asthma control without substantially increasing self-monitoring burdens for adolescent patients. Clinical Trial Registration NCT01696357. Registered 18 September 2012.