Validity of asthma diagnoses recorded in the Medical Services database of Quebec

The goal of this study was to evaluate the validity of asthma diagnoses recorded in the Medical Services (physician billing) database of the Canadian province of Quebec. The predictive positive value (PPV) and predictive negative value (PNV) of two operational definitions of asthma based on diagnoses recorded in the database were evaluated. Patients 16-80 years old treated by a respiratory or a family physician in 2002 were selected from the database. The diagnosis derived from the Medical Services database was compared to the diagnosis written in the patient's medical chart. The PPV and PNV of the first operational definition based on one asthma diagnosis or more recorded in the database over a 1-year period were found to be 0.75 and 0.96 for respiratory physicians and 0.67 and 0.99 for family physicians, for patients 16-44 years old. The PPV increased to 0.78 for family physicians and to 0.77 for respiratory physicians when the second operational definition based on two diagnoses of asthma or more was used. Results tended to be lower for 45-80 years old patients. We conclude that diagnoses recorded in the Medical Services database of Quebec are valid to identify patients with asthma.