Background Abnormal spirometry results are a leading cause of referral to secondary care in the UK. Spirometry performed in GP practices is often supervised by nursing staff and in secondary care by dedicated respiratory physiologists. We felt that patients who performed spirometry in secondary care would be encouraged to exhale to their full capacity and achieve higher spirometric values.
Methods We collected patient spirometry values from 87 GP referral letters and compared them with the values obtained at our lung function laboratory at a district general hospital. We used a paired t-test to compare the two sets of spirometry results.
Results We found that there were significant differences between the lab FEV1 (p = 0.034), FVC (p < 0.0001) and FEV1/FVC ratio (p = 0.0001) compared to primary care values. There was a 77 ml average increase in FEV1 and a 241 ml average increase in FVC when spirometry was performed in our lung function lab.
Importantly, when we looked at the individual results, 18 patients (21%) originally deemed to have restrictive spirometry had obstructive spirometry when performed in our lab. Six patients (7%) originally had obstructive spirometry which proved to be normal or restrictive in our lab.
Conclusions A significant difference was identified between GP and secondary care spirometry. The most important aspect of this is the understanding that spirometry is effort based. Most patients require significant encouragement to perform to their limit. If a less than maximal effort is made, the FVC value is most affected. This may cause truly obstructive spirometry to appear restrictive.
Primary care spirometry gave a misleading picture in 28% of cases in this cohort, resulting in instances where referrals, investigations and treatments might have been avoided and possibly managed in primary care. Effective spirometry enables more accurate diagnosis, therefore reducing the chance of under or over treatment.
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