The maximum symptom day (MSD), which has never been validated, yet has been used as a measure of asthma symptom control in inner-city populations, was recently determined to be reliable, responsive, and valid, according to a study published in the Journal of Allergy and Clinical Immunology.
Researchers used outcome data from the Mouse Allergen and Asthma Intervention Trial (n=350), which evaluated participants every 3 months for 1 year, to assess the reliability, validity, responsiveness, and predictive characteristics of the MSD. The MSD was defined as the largest value of the number of days in the prior 2 weeks that a participant reports cough, wheezing, or shortness of breath, slowed activities because of these symptoms, or nocturnal awakening as a result of these symptoms. Data included the MSD, days of rescue inhaler use in the prior 2 weeks, unanticipated asthma-related healthcare use and oral steroid use in the prior 3 months, and the Childhood Asthma Control Test (C-ACT; ages 5-11), Asthma Control Test (AC; ages 12-17), and Pediatric Asthma Therapy Assessment Questionnaire-Control Subscale (ATAQ-Control).
Internal consistency reliability was assessed by Cronbach α at all visits. Test-retest reliability was assessed by the intraclass correlation coefficient in individuals who had stable control on the ACT/C-ACT. Between baseline and the 6-month visit, this was 0.57 and 0.55 between the 6-month and 12-month visit, which indicated moderate test-retest reliability.
Criterion validity was demonstrated by identifying significant Spearman correlations between MSD and ACT/C-ACT scores, ATAQ-Control scores, and days of rescue inhaler use at all visits. The absolute mean correlations with the ACT, C-ACT, and ATAQ-Control scores were 0.71, 0.52, and 0.53, respectively.
Predictive validity was confirmed by demonstrating significant associations between MSD and risk for acute healthcare use or corticosteroid need in the following 3 months (1-day increase in MSD = 4% increase in risk for an acute care encounter; relative risk, 1.04 [95% CI, 1.02-1.06]; P <.01).
“[T]he maximum symptom day is a reliable, responsive, and valid measure of asthma symptomatology that is consistently correlated with other measures of asthma control among inner-city populations,” the researchers wrote. “Increases in maximum symptom day were associated with increased risk of subsequent asthma-related acute healthcare utilization and use of corticosteroids, without floor or ceiling effects.”
Wu TD, Perzanowski M, Peng RD, et al. Validation of the maximum symptom day among children with asthma [published online October 18, 2018]. J Allergy Clin Immunol. doi:10.1016/j.jaci.2018.10.008