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Ten tips on differentiating asthma from COPD

GP Dr David Bellamy offers expert advice on distinguishing between these two respiratory conditions

GP Dr David Bellamy offers expert advice on distinguishing between these two respiratory conditions

1 Asthma and COPD can be hard to distinguish. Asthma affects about five million in the UK – about 900,000 have been diagnosed with COPD, but estimates put the real number at about three million. Although both are chronic inflammatory disorders, pathological lung changes differ.

2 Take a detailed clinical history. Latest BTS/SIGN asthma guidelines have based diagnosis on patterns of symptoms with no other explanation. There are clinical features that suggest high, intermediate and low probabilities of asthma.

3 Base your diagnosis on features that increase the probability of asthma. In adults these are:

• more than one of the following – wheeze, breathlessness, chest tightness and cough, particularly if symptoms are worse at night or early morning, triggered by exercise or allergens, or occur after taking aspirin or ß-blockers

• a history of atopy

• a family history of asthma, hay fever or atopy

• widespread wheeze heard on auscultation

• unexplained reduced peak flow or FEV1.

4 Consider features that increase the probability of COPD. Largely a disease of over-40s, COPD is linked with a history of smoking in about 90% of cases. Men used to be more commonly affected but the gender difference is now small – it appears women are worst affected by smoke. Most COPD sufferers will have a greater than 20 pack-year history but women may have less.

5 COPD symptoms are more persistent with little day-to-day or diurnal variation. Think of COPD if there is persistent exertional breathlessness, chronic cough, regular sputum production, frequent winter bronchitis or a persistent wheeze.

6 COPD can only be confirmed with evidence of airflow obstruction on spirometry. NICE COPD guidelines define airflow obstruction as an FEV1 of below 80% predicted and an FEV1/FVC less than 0.7. For the QOF this should be measured after bronchodilator therapy. It is likely NICE will endorse this in the 2010 COPD update. Airflow obstruction alone does not distinguish asthma from COPD – the history needs to be taken into account.

7 There has been a lot of confusion about reversibility testing. After considerable discussion, asthma and COPD guidelines and the QOF now agree that an increase in FEV1 of greater than 400ml after bronchodilator or steroids suggests asthma. If this is not achieved you cannot completely dismiss asthma. COPD bronchodilator response is usually less than 200ml. Using PEF monitoring twice daily for two weeks to look for more than 20% diurnal variation is an alternative.

8 Tests other than spirometry can be useful. A chest X-ray should be taken in all new COPD patients, largely to exclude other diagnoses such as lung cancer. In both asthma and COPD there may be signs of hyperinflation and in more advanced COPD lung destruction can be noted.

An FBC may show raised eosinophils in asthma and either anaemia (normochromic) or polycythaemia in COPD. A gas transfer lung function test in secondary care is likely to be normal in asthma but reduced in COPD.

9 A look at responses to inhaled bronchodilators, inhaled steroids and two-week courses of prednisolone can help. Generally asthma patients will show greater responses, with symptoms and lung function returning towards normal. COPD patients show improved symptoms but lung function never returns to normal.

10 Refer to a respiratory specialist if diagnosis remains unclear. Late-onset asthma may take several weeks to respond to therapy. An unexpectedly large change in symptoms or lung function may suggest asthma. It is possible that some patients can be diagnosed with both asthma and COPD. Long-standing asthma may become unresponsive to bronchodilators – by definition this becomes COPD. A previous asthma sufferer should always be given asthma therapy.

Dr David Bellamy is an adviser for Bournemouth and Poole PCT, a trainer for Education for Health, a member of the General Practice Airways Group and a retired GP

Competing interests None declared

Asthma versus COPD

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