Accuracy of asthma and COPD diagnosis in Australian general practice: A mixed methods study

Background: Spirometry is the 'gold standard' for diagnosing asthma and chronic obstructive pulmonary disease (COPD) but is rarely used in general practice. Aims: To compare doctor diagnoses with patient reports/spirometry and to determine doctors' perceptions of spirometry. Methods: Patients prescribed inhaled medication were recruited from 31 practices. Doctor diagnoses were extracted from practice records. Patients completed a questionnaire and spirometry before and after bronchodilator. In-depth interviews were conducted with a sample of doctors. Results: Doctor diagnoses were available for 278 patients: asthma 192 (69%), COPD 38 (14%), asthma/COPD 40 (14%), and eight patients (3%) with other conditions. The diagnosis of asthma was correctly reported by 93% of patients, but only by 61% of those with COPD alone. Among those with both diagnoses, 83% reported asthma and 48% reported COPD. Of those with a diagnosis of COPD, 65% had fixed airflow limitation. Conversely, only 14% of those had been diagnosed with COPD alone. There was no significant difference in reversibility in forced expiratory volume in 1 second between diagnoses. While recognising the value of spirometry in differentiating between asthma and COPD, most general practices only used spirometry in diagnostically difficult cases. Conclusions: Doctor-diagnosed asthma is accurately reported by patients. However, COPD remains substantially under-diagnosed. Spirometry needs to be more widely used to improve the accuracy of respiratory diagnoses in general practice.