Impact of body mass index on the predictive capacity of the COPD-6 device in the detection of airflow obstruction

Abstract

Background and objective: The portable COPD-6 device has been validated as a screening tool for airflow obstruction through the quantification of the FEV₁/FEV₆ ratio. To date, however, the impact of body mass index (BMI) on its ability to predict airflow obstruction has not been evaluated. The aim of the study was to assess the predictive ability of COPD-6 to detect airflow obstruction based on the patient's BMI.

Material and method: A prospective and open cohort study in which 223 subjects who underwent conventional spirometry and COPD-6 were included. The area under the curve ROC (AUC) of FEV₁/FEV₆ was analysed in the detection of obstruction for all patients in addition to BMI (BMI<30kg/m² and BMI≥30kg/m²). Sensitivity and specificity, negative and positive predictive value as well as likelihood ratio were calculated to determine the cut-off point of COPD-6 FEV₁/FEV₆ ratio with greater predictive capacity.

Results: The COPD-6 allows ruling out airflow obstruction with AUC of the estimated ROC curve of 88% (95% CI 83-93). The cut-off point FEV₁/FEV₆ of 0.74-0.76 shows the best predictive capacity. However, this capacity is altered according to BMI with an increase in false positives in subjects with BMI≥30kg/ m² when using the same cut-off point for the whole sample.

Conclusion: The choice of cut-off point FEV₁/FEV₆ for the detection of obstruction should be adjusted to the patient's BMI.

Keywords: Body mass index; Chronic obstructive pulmonary disease; Enfermedad pulmonar obstructiva crónica; Espirometría; FEV(6); Spirometry; Índice de masa corporal.