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NICE spirometry definitions lead to 'overdiagnosis' of COPD

06-Oct-08

Current COPD guidance may lead to overdiagnosis of the condition, an analysis of spirometry results from 14,056 patients suggests.

Dutch researchers looked at which patients would be diagnosed with COPD if a fixed cut-off definition of airway obstruction was used, as is recommended by NICE and other COPD guidelines, compared with a definition adjusted for age and sex.

Using spirometry data from 330 GPs in the Netherlands, they found that the fixed definition led to misdiagnosis in around a quarter of patients. The proportion of patients misdiagnosed increased with age, from 15.5 per cent for those 41-50 years old, to 42.7 per cent for those aged over 81.

Overdiagnosis of airway obstruction could mean patients are incorrectly diagnosed and treated for COPD, the researchers said.

NICE guidelines define COPD by the presence of airflow obstruction, as demonstrated by a lung function score under 70 per cent of expected for either FEV1 or forced vital capacity (FVC).

The researchers compared the diagnosis rate using this fixed score with a definition based on whether patients' FEV1 or FVC was below the lower limit of normal for their age or sex.

Jane Scullion, consultant nurse in Leicester and chair of the Nurse Advisory Group for the British Thoracic Society, said: 'The problem is that the expected FEV1 is based on averages, so you have people at either end of the range.

'There will be people with a reduced FEV1 who have no symptoms, and may not have COPD in a clinical sense, and people who are symptomatic yet have a normal FEV1, who may have COPD and benefit from treatment.'

She said it was important to remember that spirometry only provides you a measurement, and that a diagnosis was all about the patient.

'A patient's clinical history, smoking history and occupation all need to be taken into account when assessing them and deciding whether they should be treated for COPD,' Ms Scullion said.

Loughborough GP Dr Dermot Ryan added that although spirometry was crude, it was 'cheap, accessible and reliable', and effective if used alongside good clinical judgment.