Pediatric asthma surveillance using Medicaid claims.

Objective: The purpose of this study was to describe the prevalence of asthma among children using alternative case definitions applied to administrative claims data, and to assess year-to-year classification concordance.

Methods: This study was a retrospective cohort analysis of 357,729 children 0-18 years using 2001-2002 Michigan Medicaid claims. Asthma cases were classified using six alternative definitions based on outpatient, emergency department, inpatient, and pharmacy claims for asthma, including the Health Plan Employer Data Information Set (HEDIS) persistent asthma criteria commonly used for assessments of asthma health care quality: at least one asthma inpatient admission or emergency department visit, four or more asthma medications events, or four asthma outpatient visits and two asthma medication events.

Results: Overall, asthma prevalence varied widely between alternative case definitions, ranging from 14.9% based on claims evidence of any type of asthma utilization to 3.7% when restricted to those with four or more asthma medication dispensing events. Among cases meeting HEDIS persistent asthma criteria in 2001, 55.5% met these criteria in 2002. Those with four or more asthma medication dispensing events had the best overall classification concordance between 2001 and 2002. Utilization of asthma services and prevalence estimates were highest among children younger than 5 years old, but year-to-year classification concordance was poorest among these cases (p < 0.0001), irrespective of case definition.

Conclusions: While overall asthma prevalence may remain relatively stable from year to year, individuals may not be classified consistently as cases over time, regardless of case definition. Studies that identify asthma cases in one year and assess asthma outcomes in a subsequent year may introduce substantial bias as a result of case misclassification. Among the case definitions considered in this study, our findings suggest that this bias is minimized among cases classified using the four or more asthma medication dispensing events criterion.