Can a simple lung monitor be used as a screening test for COPD in primary care?
COPD is widely underdiagnosed worldwide; there is a drive to identify and treat patients earlier. Diagnostic spirometry is not widely available in many countries. The lung monitor is a simple screening test which measures FEV1/FEV6 and could be used as a screening step in primary care to identify patients suitable for spirometry referral.
Our aim was to assess the performance of a simple post bronchodilator (postBD) COPD screener device compared to postBD quality diagnostic spirometry, amongst primary care patients. We conducted a nested case-control study within the Birmingham COPD Cohort study. Patients with chronic respiratory symptoms at the final visit received postBD lung function assessment with the Vitalograph lung monitor (Index) followed by the nddEasy One spirometer (Reference). Cases were defined using the lower limit of normal (LLN - GLI), based on gold standard spirometry data. Correlation, agreement and discrimination (c statistic) was calculated.
546 patients had reference and index test data. Reference and index tests were highly correlated for FEV1 (r=0.97; p<0.001) and FEV6(screener) with FVC(spirometry) (r= 0.91; p<0.001). 325 (59.5%) patients had airflow obstruction according to the reference test. The index test showed good discrimination (C=0.92; 95% CI 0.89, 0.94). Using the LLN as the cut-off, the index test had only 32.9% sensitivity (95% CI 27.8%, 38.3%) but 98.6% specificity (95% CI 96.1%, 99.7%); (PPV=97.3%, NPV=50.0%).
Excellent correlation was observed between the postBD lung monitor and diagnostic spirometry, however the optimum cut-off for the lung monitor should be identified as use of the LLN cut-off has low sensitivity. Among patients with respiratory symptoms, the lung monitor could potentially be used as an initial screener to identify those warranting diagnostic spirometry.