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Is spirometry for asthma practical in primary care?

Thank you for Dr Graham Douglas' article ‘Updated asthma guideline will improve outcomes' (Practitioner 2008;252[1710]:33-39), which discussed the newly updated BTS/SIGN British Guideline on the Management of Asthma.

The guideline advises using spirometry, rather than peak flow, as the preferred measure of lung function. However, in practice this would inundate our spirometry clinic, which we use to diagnose COPD as recommended in the QOF.

The diagnosis of asthma is clinical.

I think most GPs will continue using peak flow as a measure of lung function. What are Dr Douglas' views regarding the practicality of this recommendation for GPs?

Dr Hastie Salih, GP, Essex

Dr Graham Douglas replies:

The recently updated British Guideline on the Management of Asthma advocates the use of spirometry, rather than peak flow, in the diagnosis of asthma for several reasons.

First, spirometry allows clearer identification of airflow obstruction, which implies a diagnosis of either asthma or COPD. Low peak flow can also be found in other causes of breathlessness, such as heart failure, interstitial lung diseaseand pneumothorax.

Second, spirometry results are less dependent on effort and are therefore more consistent than peak flow.

Results from spirometry are also useful if the initial history and examination leave uncertainty about the diagnosis.

In such cases the differential diagnosis and approach to investigation is different in patients with and without airflow obstruction.

In patients with a normal or near-normal spirogram, potential differential diagnoses are mainly non-pulmonary, and these conditions are unlikely to respond to inhaled steroid or bronchodilator therapy.

In contrast, in patients with a spirogram suggesting obstruction the question is less whether they will need inhaled treatment but rather exactly what form and how intensive this should be.

Spirometry is becoming widely available in primary care to identify patients with COPD who are or may have been smokers. The skills required to perform and interpret spirometry are, I believe, improving across the UK.

It is important to emphasise that the new BTS/SIGN guideline has been written with considerable input from primary care, specialist respiratory nurses and the GPIAG, who all believe this is a reasonable way forward for making a firm diagnosis of asthma. Such a diagnosis in adults may lead to lifelong therapy and it is therefore crucial that the initial diagnosis is made on the best possible evidence.

Daily peak flow measurements over several weeks remain important for patients with adult-onset asthma in trying to identify an occupational component.

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