Utility of the neutrophil-to-lymphocyte ratio for predicting bacterial infection in patients with rheumatoid arthritis receiving Tocilizumab

This study aimed to describe the utility of the neutrophil-to-lymphocyte ratio (NLR) for predicting bacterial infections in patients with rheumatoid arthritis (RA) treated with Tocilizumab (TCZ). We extracted RA patients treated with TCZ in whom an infection developed between April 2008 and March 2018 from our hospital database. We divided these patients into the bacterial infection and non-bacterial infection groups and compared their background, C-reactive protein (CRP) values, white blood cell count (WBC), the NLR at the time of infection diagnosis, and the ratio of the NLR at the time of infection diagnosis (post-NLR) to the NLR at baseline (pre-NLR). Of the 196 patients who received TCZ, 21 experienced a bacterial infection and 20 had a non-bacterial infection. The median CRP level, WBC count, post-NLR, and post-NLR/pre-NLR ratio in the bacterial infection group were significantly higher than in the non-bacterial infection group. In receiver operating characteristics (ROC) curve analysis for predicting bacterial infection, the area under the curve (AUC) for CRP, WBC, NLR, and the post-NLR/pre-NLR ratio were 0.787, 0.857, 0.887, and 0.975, respectively. The cut-off value of 2.25 for the post-NLR/pre-NLR ratio showed the greatest sensitivity (90.5%) and specificity (100%). The post-NLR/pre-NLR ratio may be a useful surrogate marker for predicting bacterial infections in patients with RA treated with TCZ.