Background The use of administrative databases to perform epidemiologic studies in the field of asthma has expanded in recent years. The unavailability of clinical parameters to measure the level of asthma severity and control is considered as one of the major limitations of database studies. The aim of our study was to develop and validate two database indexes, one to measure the control of asthma and the other to measure asthma severity.
Methods The database index of asthma severity (3 categories) and the database index of asthma control (2 categories) were derived from the definitions found in the Canadian Asthma Consensus Guidelines and were based upon dispensed prescriptions (controller therapies, short- acting beta2-agonists, oral corticosteroids) as well as the medical services for asthma (ED visits and hospitalizations), which were recorded in two large administrative databases from the Canadian province of Quebec; Régie de l'Assurance Maladie du Quebec (RAMQ) and MED-ECHO over 12 months. For validation purposes, 71 asthmatic patients were randomly selected from two asthma clinics and their spirometric lung function measures were retrieved from their medical chart. For these patients, we also obtained data on prescriptions and medical services from the aforementioned databases. The database indexes of asthma severity and control were validated against the pulmonary function test results using t-tests. Our database indexes of asthma severity and control were also applied in the Quebec cohort which was comprised of 139 283 person-years of follow-up of asthmatic patients who were selected from RAMQ and MED- ECHO databases between January 1st 1997 and December 31st 2004.
Results According to the database indexes, 49.3%, 29.6% and 21.1% of patients recruited at the asthma clinics were found to respectively have mild, moderate and severe asthma while 53.5% were found to have controlled asthma. The mean predicted value of the forced expiratory volume in one second (FEV1) ranged from 89.8% for mild asthma to 61.5% for severe asthma (p-value<0.001) whereas the range from controlled to uncontrolled asthma was 89.5% to 67.3% (p-value<0.0001). The ratio of the FEV1 to the forced vital capacity (FEV1/FVC ratio) was measured for 56 patients and ranged from 75.8% for mild asthma to 61.8% for severe asthma (p-value of pairwise comparison=0.030) whereas the range from controlled to uncontrolled asthma was 75.3% to 65.7% (p-value =0.0009).
Conclusions In the absence of clinical data, our database indexes could be used in epidemiologic studies using administrative databases that record data on dispensed prescriptions and medical services for asthma to reasonably assess the severity and control of asthma.
- Administrative databases
- Asthma control
- Asthma severity