• Spirometry used for diagnosing COPD and asthma in children aged >5 and adults

• FEV1: the volume of air that the patient is able to exhale in the 1st second of forced expiration

• FVC: the total volume of air a patient can forcibly exhale in 1 breath

• FEV1/FVC: the ratio of FEV1 to FVC expressed as a percentage

• These values apply to Caucasians: reduce values by 7% for Asians and 13% for Afro-Caribbeans. If aged ≥70 see equations in: https://www.brit-thoracic.org.uk/document-library/delivery-of-respiratory-care/spirometry/spirometry-in-practice/ : 

• Spirometry (British Thoracic Society), Spirometry (NHS Choices), Peakflow.com, Peak flow (NHS Choices)​, Peak flow diary (asthma.org.uk)

​Interpretation

• Normal: FEV1/FVC around 75%

• Abnormal if FEV1 or FVC <80% predicted or FEV1/FVC <0.7

• Obstructive disease: FEV1 <80% predicted and FEV1/FVC <70%: Asthma, COPD (COPD has less reversibility compared to asthma), Bronchiectasis: Bronchiectasis (CKS), Bronchiectasis (NHS Choices), , Cystic fibrosis: Cystic fibrosis (NHS Choices)

• Restrictive disease: FEV1/FVC often >70%, but both are decreased e.g. Asbestosis: Asbestosis (NHS Choices), Aspergillosis: Aspergillosis (NHS Choices), Hypersensitivity pneumonitis / Extrinsic allergic alveolitis: Hypersensitivity pneumonitis (British lung foundation), Pneumonitis (patient.info), Pulmonary fibrosis: Pulmonary fibrosis (NHS Choices), Silicosis: Silicosis (NHS Choices)​