Typical symptoms of COPD such as cough, wheezing and difficulty breathing are common to asthma, too, and someone may have both conditions. However, age of onset can be an indicator.[4,5]

NICE says to suspect COPD in people over 35 who have a risk factor (especially smoking or history of smoking) and who present with one or more of the following symptoms:[4]

• exertional breathlessness;
• chronic cough;
• regular sputum production;
• frequent winter ‘bronchitis’;

Global guidelines add that shortness of breath or dyspnoea in COPD is persistent, progresses over time and worsens with exercise. Chronic cough may be intermittent and may not necessarily be productive.[7]

Other signs and symptoms to ask about include weight loss, reduced tolerance to exercise, breathlessness while sleeping, tiredness, swollen ankles, and possible exposure to pollutants or occupational exposure. Chest pain and coughing up sputum containing blood (haemoptysis) are uncommon in COPD so may point to other diagnoses.[4]

Testing sputum to identify infective organisms may be needed if sputum production is sustained and purulent.

Another possible investigation is to assess the oxygen exchange from the lungs into the blood using a gas transfer test to assess the transfer factor or diffusing capacity. The transfer capacity of the lung for the uptake of carbon monoxide (TLco) test uses air containing carbon monoxide (0.3%) and an inert carrier gas such as helium. It measures the change in concentrations between inhaled and exhaled air.[4,11,12]

In COPD, low readings can indicate the destruction of alveoli in emphysema (whereas chronic bronchitis will have normal readings). Low TLco levels can also result from smoking (smokers should abstain for at least 24 hours before taking the test) and interstitial lung diseases such as pulmonary fibrosis due to scarring thickening the alveolar-capillary membrane.[12]

High TLco levels can occur with asthma or obesity, with large lung volumes, as well as conditions such as systemic lupus erythematosus and conditions where there is pulmonary haemorrhaging.