Spirometry is fundamental to making a diagnosis of COPD and a confident diagnosis of COPD can only be made with spirometry. However, there is no single diagnostic test for COPD. Making a diagnosis relies on clinical judgement based on a combination of history, physical examination and confirmation of the presence of airflow obstruction using spirometry.
Spirometry is the only accurate method of measuring the airflow obstruction in patients with COPD. Peak expiratory flow rate (PEFR) measurement may significantly underestimate the severity of the airflow limitation.
A diagnosis of airflow obstruction can be made if the FEV1/FVC <0.7 (ie 70%) and FEV1 <80% predicted.
National Institute for Health and Clinical Excellence (NICE) classification of the severity of COPD:
- Stage 1 - mild: 80% or above (symptoms should be present to diagnose COPD in people with mild airflow obstruction).
- Stage 2 - moderate: 50-79%.
- Stage 3 - severe: 30-49%.
- Stage 4 - very severe: below 30% (or FEV1 less than 50% but with respiratory failure).
The presence of airflow obstruction should be confirmed by performing post-bronchodilator spirometry.
Changes in the flow volume loop may give additional information about mild airflow obstruction.
For more on Spirometry in Primary Care, read more here.