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

Spirometry is the 'gold standard' for diagnosing asthma and chronic obstructive pulmonary disease (COPD) but is rarely used in general practice.

To compare doctor diagnoses with patient reports/spirometry and to determine doctors' perceptions of spirometry.

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.

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.

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.