Relationship of Red Cell Index with the Severity of Chronic Obstructive Pulmonary Disease

We aimed to investigate the association between red cell index (RCI) and the severity of Chronic Obstructive Pulmonary Disease (COPD), and compare predictive value of RCI, neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) for the severity of COPD.

A total of 207 participants were recruited (100 COPD patients and 107 healthy controls). COPD patients were divided into two groups according to the optimal cut-off value of RCI determined by the receiver operating characteristic (ROC) curve. Pearson's correlation test, logistic regression analysis and other tests were performed.

Compared with low RCI group, the forced expiration volume in 1 second (FEV₁) and FEV₁ in percent of the predicted value (FEV₁%) in high RCI group were lower (p = 0.016, p = 0.001). There was a negative correlation between RCI and FEV₁% (r = -0.302, p = 0.004), while no correlation between FEV₁% and NLR as well as PLR were found. RCI showed higher predictive value than NLR and PLR for predicting Global Initiative for Chronic Obstructive Lung Disease classification (GOLD), with a cut-off value of 1.75 and area under the curve (AUC) of 0.729 (p = 0.001). Multivariate logistic regression analysis proved that RCI was an independent factor for lung function in COPD patients (odds ratio [OR] = 4.27, 95% CI: 1.57-11.63, p = 0.004).

RCI is a novel biomarker that can better assess pulmonary function and severity of COPD than NLR and PLR. Higher RCI is related to deterioration of pulmonary function.