Interpreting the diagnostic accuracy of tools for early detection of COPD

Abstract

There has been increasing interest in recent years in developing and testing strategies for early detection of chronic obstructive pulmonary disease (COPD) in primary care. Proponents of early detection argue that COPD is underdiagnosed and should be detected early because of its irreversible and progressive nature.1 Opponents, on the other hand, argue that early detection primarily yields subjects with mild to moderate airflow limitation and that medical services do not have the capacity to provide care for patients with borderline abnormal spirometry.2 In this issue of the PCRJ, two studies present findings on a potential new tool for early detection of COPD -the PiKo-6 ® expiratory flow meter (or 'mini-spirometer') -and compare this with an existing strategy -a COPD diagnostic questionnaire. 3,4The PiKo-6 ® (nSpire Health Inc.) is a relatively new and simple screening device that measures the forced expiratory volume in one and six seconds (FEV1 and FEV6, respectively) and the FEV1/FEV6 ratio. The device provides audio-visual feedback on the duration and quality of the exhalation manoeuvre and shows results immediately on a small display. Subjects below a certain threshold of FEV1/FEV6 (e.g., <0.70 pre-or post-bronchodilator) are considered "at risk" of COPD.An international group of primary care specialists developed a COPD diagnostic questionnaire which has been implemented by the International Primary Care Airways Group (this questionnaire is further referred to as the "IPAG questionnaire" throughout this text). 5,6 The questionnaire comprises eight items and its scoring system permits the calculation of an overall COPD risk score ranging from 0 -38 points. Subjects with more than 16.5 points are considered "at risk" of COPD. 6In the two studies from Sichletidis et al. 3 and Frith et al. 4 , the diagnostic accuracy of the IPAG questionnaire and the PiKo-6 ® were tested against the "gold standard" -i.e., spirometry according to ATS/ERS guidelines, with post-bronchodilator FEV1/forced vital capacity (FVC) <0.70 defining COPD. 7In the first study, Sichletidis et al. screened 1,078 current, former and never-smoking patients aged older than 40 years without prior diagnosis of COPD, 49% of whom were current smokers. 3 The prevalence of COPD was 10% (of which 84% was mild-to-moderate disease). For patients with PiKo-6 ® post-bronchodilator FEV1/FEV6< 0.70, sensitivity (SN) and specificity (SP) were SN=80% and SP=95%. For patients with IPAG >16.5 points, these measures were SN=91% and SP=49%.In the second study, Frith et al. screened 204 current and former smoking patients aged 50 or older without prior diagnosis of COPD, 45% of whom were current smokers. 4 The prevalence of COPD was 28% (of which 95% was mild-to-moderate COPD). For patients with PiKo-6 ® pre-bronchodilator FEV1/FEV6< 0.75, the diagnostic accuracy measures were SN=81% and SP=71%. For patients with IPAG > 16.5 points, these measures were SN=91% and SP=37%.How can we interpret these different measures of diagnostic accuracy? Most diagnostic tes...

COPD Diagnostic Questionnaire (CDQ) for selecting at-risk patients for spirometry: a cross-sectional study in Australian general practice

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Insight into Best Variables for COPD Case Identification: A Random Forests Analysis

“…31, 32 Higher levels of sensitivity will permit fewer missed patients, with the added costs of spirometric testing in people without clinically significant COPD; greater specificity will result in more missed cases, but fewer false positives and lower overall screening costs. 33 These analyses attempted to identify the best and smallest set of predictors capable of differentiating cases and controls under 4 scenarios, optimizing the balance between number of variables and precision.…”

Spirometry: an essential tool for screening, case-finding, and diagnosis of COPD

“…Kotz and van Schayck, 8 in an accompanying editorial to the Frith 9 and Sichletidis 10 articles, eloquently describe the necessity for higher sensitivity at the risk of losing specificity in order to minimise falsenegatives. In other words, maximising the chances of positively identifying COPD means that more patients would have to be referred for confirmatory diagnostic spirometry, arguably unnecessarily.…”

“…7 There are considered perspectives available from both proponents and opponents to the concept of COPD case-finding in primary care -as previously debated and then summarised recently in this journal. 8 Furthermore, there is no consensus as to which casefinding method is best -microspirometry versus standard spirometry -and whether these should be performed either pre-or postbronchodilator [8][9][10] and with or without questionnaire screening.…”

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