Background. FEV1/FEV6 has been proposed as a cheap, reproducible and valid alternative to FEV1/FVC in spirometry. No Indian data exists on its utility to diagnose airway obstruction. Aim. we sought to determine a fixed cut off of FEV1/FEV6 to diagnose obstruction corresponding to FEV1/FVC < 0.70 proposed by GOLD guidelines. Method. Spirometry was done on patient referred to a tertiary centre in India. Age, sex, height weight were recorded in addition to spirometric variables like FEV1, FVC, FEV6. The sensitivity, specificity, positive and negative predictive values of FEV1/FEV6 were determined with respect to gold standard of FEV1/FVC < 0.70. Results. 467 spirometries were analysed after meeting the ATS acceptability criteria. Considering FEV1/FVC < 0.7 as being the gold standard for obstruction, ROC curve was used to determine the best corresponding cut-off for FEV1/FEV6. The area under the curve was 99.3% (95% CI: 98.1–99.8%), and the FEV1/FEV6 cut-off, corresponding to the greatest sum of sensitivity and specificity, was 73%. For the total population, the FEV1/FEV6 sensitivity, specificity, PPV, NPV were was 95.7 %, 94.2 %, 87.5 % and 97.9 % respectively. Agreement by Kappa value between two cut offs was excellent 0.89 (0.87–0.91). Conclusion. FEV1/FEV6 < 73% is a new reliable spirometry index to diagnose airway obstruction in Indian population. 1. Introduction Undiagnosed airway obstruction is prevalent in smokers and occupational settings, leading to significant morbidity and adverse prognosis [1]. Many studies underline the importance of spirometry in primary care, as a screening tool for the early detection of COPD in all patients greater than forty years of age who are currently smoking as well as those with respiratory symptoms [2–5]. Forced expiratory volume in six seconds (FEV6) [6] has been proposed as a convenient alternative for forced vital capacity (FVC) [7–10]. The advantages of FEV6 described in the literature are easy execution (for patients and technicians) [11], reduction in the total duration of the spirometry test, and reduction in spirometry complications (such as syncope) [12, 13]. Studies show that the criteria adopted to define obstruction from the FEV1/FEV6 ratio are quite variable like LLN derived from reference equations [10–16] ROC curve analysis to find the best cutoff point [17, 18], and an empiric fixed FEV1/FEV6 ratio of 0.70 [19]. In developing countries due to lack of trained technicians in primary care who can effectively perform FVC with costly spirometers, FEV6 promises to be a cheap, effective measure to use
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