THEY are known as the missing millions. Around one million people have been diagnosed with COPD, a collection of lung diseases including chronic bronchitis, emphysema and chronic obstructive airways disease, yet according to Dr Dinesh Saralaya, consultant respiratory physician at Bradford Royal Infirmary, many more remain undiagnosed.

One of the issues, he explains, is that many smokers relate their cough to smoking and often delay going to see their doctor.

"We have always known it is undiagnosed and that is why, very often, they are called the missing millions. We think there are about one million sufferers with COPD but two to three million remain undiagnosed and the reason is because awareness of the disease is only appearing now.

"If smokers have a cough they are late going to their GP because they attribute their symptoms to smoking," explains Dr Saralaya, who is also associate director for research and divisional clinical lead Yorkshire and Humber clinical research network.

While abnormal lung function gives a firm diagnosis, Dr Saralaya says around 80 per cent have a mild form of the disease and don't fulfil the criteria for having an abnormal lung function.

Most people are not diagnosed until they are in their 50s, but people over the age of 35 are often affected.

According to research published in the BMJ, current guidelines mean that chronic obstructive pulmonary disease is being over-diagnosed in older men and under-diagnosed in younger women.

Professor Martin Miller and Dr Mark Levy said their research has found that up to 13per cent 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 Birmingham University, and Dr Levy, a GP, 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."

Dr Saralaya believes increased awareness could also play a crucial part in prompting people to seek medical advice sooner, rather than later.

Quitting smoking would also help to tackle the disease. For those who have given up smoking and are concerned about their cough, or if they are finding they are out of breath doing relatively simple activities such as climbing stairs, he urges them to see their GP or practice nurse as soon as possible.

Around five to 10 per cent of sufferers may never have smoked but the cause of their condition could be down to careers such as working in coal mines or being exposed to particular dusts.

"We need to raise the profile of the disease," says Dr Saralaya.

"We have a very vibrant clinical trials unit in Bradford, we have got world class research happening in Bradford and it is about raising awareness and making sure patients can take part in these trials."