Childhood asthma surveillance using administrative data: consistency between medical billing and hospital discharge diagnoses.

BACKGROUND: The absence of ongoing surveillance for childhood asthma in Montreal, Quebec, prompted the present investigation to assess the validity and practicality of administrative databases as a foundation for surveillance.
OBJECTIVE: To explore the consistency between cases of asthma identified through physician billings compared with hospital discharge summaries.
METHODS: Rates of service use for asthma in 1998 among Montreal children aged one, four and eight years were estimated. Correspondence between the two databases (physician billing claims versus medical billing claims) were explored during three different time periods: the first day of hospitalization, during the entire hospital stay, and during the hospital stay plus a one-day margin before admission and after discharge ('hospital stay +/- 1 day').
RESULTS: During 1998, 7.6% of Montreal children consulted a physician for asthma at least once and 0.6% were hospitalized with a principal diagnosis of asthma. There were no contemporaneous physician billings for asthma 'in hospital' during hospital stay +/- 1 day for 22% of hospitalizations in which asthma was the primary diagnosis recorded at discharge. Conversely, among children with a physician billing for asthma 'in hospital', 66% were found to have a contemporaneous in-hospital record of a stay for 'asthma'.
CONCLUSIONS: Both databases of hospital and medical billing claims are useful for estimating rates of hospitalization for asthma in children. The potential for diagnostic imprecision is of concern, especially if capturing the exact number of uses is more important than establishing patterns of use.