Thousands of people are being misdiagnosed with chronic lung disease, health experts have warned.
Current guidelines mean that chronic obstructive pulmonary disease (COPD) is being over-diagnosed in older men and under-diagnosed in younger women, according to research published in the BMJ.
COPD is the name for a collection of lung diseases including chronic bronchitis, emphysema and chronic obstructive airways disease, and the main cause is smoking. The chances of developing COPD increases with the amount and duration smoked and the cost to the NHS is around £800 million a year.
Most people are not diagnosed until they are in their 50s but people over the age of 35 are often affected, and while an estimated three million people have the disease in the UK only around 900,000 have been diagnosed, according to NHS Choices.
Professor Martin Miller and Dr Mark Levy said their research has found that up to 13% of patients thought to have the condition are actually misdiagnosed.
They said the global initiative for obstructive lung disease (Gold), which was set up to raise awareness and improve treatment, set out a number of measures for how the conditions should be diagnosed.
These have been adapted by the National Institute for Health and Care Excellence (Nice), so are used in the UK, but the pair argue that the diagnostic threshold for airway obstruction misses one in eight cases that were identified by the former method, known as the lower limits of normal (LLN).
They said this is particularly happening in younger women, with misdiagnosis leading to patients being given incorrect treatment or inappropriate medication.
For instance, the use of inhaler treatment for COPD increases the likelihood of developing severe pneumonia so people who are using them without reason are being put at increased risk, while resources are also being wasted.
They also said that people who meet only the Gold criteria have a higher prevalence of heart disease than people who meet both LLN and Gold measures.
Prof Miller, of the Institute of Occupational and Environmental Medicine at the University of Birmingham, and Dr Levy, a GP based in London, said clinicians should use the LLN method of diagnosis instead.
"Since the Gold strategy documents were published almost all COPD research work has followed their lead without asking about their validity versus other established methods for assessing COPD," they wrote.
"This needs to be corrected.
"The current Nice guidelines and the Gold strategy documents for COPD should be modified because they over-diagnose COPD in older men while missing the possibility of diagnosing heart disease; they also under-diagnose COPD in young women.
"We argue that clinicians should use the LLN instead when assessing patients for COPD."