PURPOSE OF THE STUDY.
To develop and validate a new instrument, the Composite Asthma Severity Index (CASI), which accounts for impairment, risk, and amount of medication to maintain control. Previous instruments do not take into account these measures in defining severity as outlined by the Expert Panel Report—3: For the Diagnosis and Management of Asthma.
Data from 546 children and adolescents in the Asthma Control Evaluation (ACE) trial were used initially to determine outcome domains of asthma. External validation of the severity index was achieved by using data from 419 children and adolescents in the Inner City Anti-IgE Therapy for Asthma (ICATA) trial, a double-blind, placebo-controlled multicenter trial of omalizumab versus placebo.
Factor analysis was used to determine independent outcome domains of asthma using the data from the ACE trial. Next, 26 Inner City Asthma Consortium (ICAC) clinical investigators combined and weighted the domains into a final CASI score using a Delphi consensus process. The scale properties of CASI were then evaluated for construct validity (variability at different time points compared with variability of other asthma outcomes), internal consistency, and test-retest reliability. Finally, CASI was externally validated by using data from the ICATA trial.
Five independent asthma domains out of 11 outcomes were determined and in combination accounted for 76% of the variance in the original data. These were reorganized to be compatible with present guidelines and reports resulting in the following domains with weights and maximum points allotted: days of symptoms and albuterol use (15%, 0–3 points), nights of symptoms and albuterol use (15%, 0–3 points), controller treatment (25%, 0–5 points), lung function (15%, 0–3 points), and exacerbations (includes oral corticosteroid burst and hospitalizations; 30%, 0–6 points). Final scores ranged from 0 to 20. At the ACE enrollment, the mean CASI score was 6.2 (SD = 3.0) and decreased by 23% after 3 weeks of guidelines-based intervention before randomization, mainly due to lower symptoms. After randomization and the final ACE visit 1 year later, the CASI score remained stable but redistributed to be higher in medication use and lower in symptoms. CASI was also more stable between visits compared with ACT. When externally validated by using data from ICATA, the CASI demonstrated a 0.67-point improvement in those on omalizumab and a 32% greater magnitude of effect compared with symptom days alone.
CASI provides an instrument to measure asthma severity as composite measure of control (risk and impairment) and the treatment required to achieve it.
This is the first composite asthma index to account for future risk and impairment along with the level of treatment, resulting in a comprehensive measure of severity that follows the Expert Panel Report—3 guidelines. Given the stability in the score over time, it is unique in that it can discriminate those with severe asthma even when well controlled under guidelines-directed therapy. CASI also shows greater effect sizes compared with symptom days alone because it measures the multidimensional aspect of asthma. This makes it useful in studies of new medications and changes in environmental exposure. It will also likely be practical in a clinical setting to help highlight risk and impairment when making management decisions. Additional validation in other populations is needed, and determining what constitutes an elevated CASI score or a clinically significant difference in scores remains an issue.
- Copyright © 2012 by the American Academy of Pediatrics