Why is asthma so difficult to diagnose?

Asthma is a chronic inflammatory respiratory disease. It can affect people of any age, but often starts in childhood.

It is characterised by attacks of breathlessness and wheezing, with the severity and frequency of attacks varying from person to person. The attacks are associated with variable airflow obstruction and inflammation within the lungs, which if left untreated can be life-threatening, however with the appropriate treatment can be reversible.

However, the National Institute for Health and Care Excellence (Nice) on Wednesday said studies showed up to 30 per cent of the 4.1m people treated for asthma in the UK did not show any “clear evidence” of the incurable condition and may be receiving unnecessary treatment.

A previous study also found that asthma patients were dying needlessly as a result of complacency. Three people die from asthma every day in the UK, while someone suffers from a potentially life-threatening attack every 10 seconds. But experts from the Royal College of Physicians (RCP) said a large number of deaths caused by asthma could have been prevented.

The report in 2014 found that that patients were not receiving adequate advice and information on managing their asthma, and that medics were failing to spot key signs which indicate patients are not managing their condition well.

Symptoms

There are several signs and symptoms associated with asthma:

• Wheezing
• Cough
• Shortness of breath
• Chest tightness

Although at one time these symptoms were likely to have been under-interpreted (leading to under-diagnosis or delayed diagnosis), now they are over-interpreted (leading to over-diagnosis if not supported by objective tests). The diagnostic test accuracy of asking about asthma signs and symptoms is currently uncertain.

Asthma signs and symptoms can vary from mild, moderate to severe. They can also vary throughout the year depending on the season or exposure to variable environmental triggers, such as viral infections, allergens and air pollution. They also vary with age.

Allergies

There is considerable overlap between hay fever, eczema, asthma and food allergies. However, the link between these different atopic disorders is not well understood. Therefore, as these conditions often co-exist in the same individual and family it is sometimes difficult to recognise symptoms of asthma.

Exercise

Symptoms of cough, wheeze and chest tightness often occur after exercise in many people with asthma, and also in some people who do not have asthma. The symptoms are associated with prolonged exercise, such as long-distance running, rather than short bursts of intensive exercise.

Classically, symptoms occur a few minutes after stopping exercise rather than during exercise, and can vary from mild symptoms to an acute asthma attack.

Drugs

Certain drugs are known to increase asthma in a proportion of patients. The drugs that are commonly associated with worsening of underlying asthma are aspirin, ibuprofen, and beta-blockers. Cross-sectional studies suggest that less than 10 per cent of people with asthma have worsening of their respiratory symptoms after ingestion of these drugs. However, there were no relevant clinical studies identified of clinical history of symptoms after taking aspirin or beta blockers compared with the reference standard of physician diagnosis or other objective tests in adults.

Work

Occupational asthma is a form of asthma attributable to a particular exposure in the workplace and not due to stimuli encountered outside the workplace. The true frequency is unknown, but there are concerns that it is under-reported. Published evidence estimates that occupational asthma may account for between 9 and 15 per cent of adult onset asthma. Occupational asthma is the commonest industrial lung disease in the developed world.

Diagnosis

There is currently no “gold standard test” available to diagnose asthma; diagnosis is principally based on a thorough history taken by an experienced clinician. Doctors do follow guidelines but, until now, these have been based largely on experience and expertise rather than clinical evidence. A number of methods and assessments are available to determine the likelihood of asthma.

These include measuring airflow obstruction (spirometry and peak flow) and assessment of reversibility with bronchodilators, with both methods being widely used in current clinical practice. However, normal results do not exclude asthma and abnormal results do not always mean it is asthma, as they could be indicators of other respiratory diseases or spurious readings.

Nice guidelines

The Nice guideline, published on Wednesday for consultation, stresses that to achieve an accurate diagnosis clinical tests should be used as well as checking for signs and symptoms. The process that the healthcare professional should follow in the initial assessment, and the tests to use, are presented in the guidance as simple flow charts. The first test should be carried out using a spirometer. 
Further breath tests should be carried out depending on the results from spirometry and the patient’s age. For adults and young people over five years, tests include checking for levels of nitric oxide and whether standard medicines that widen the airways of the lung are of benefit. 
The treatment of under-fives should be based on professional judgement and observation until the child is old enough to take clinical tests, said the guidance. The draft guideline also recommends that healthcare professionals should ask employed people how their symptoms are affected by work to check if they may have occupational asthma.