Is the neutrophil-to-lymphocyte ratio a useful indicator of bacterial infection in patients with RA treated with tocilizumab?

This study investigated the neutrophil-to-lymphocyte ratio (NLR) as an indicator of infection in patients with rheumatoid arthritis (RA) treated with tocilizumab (Actemra). They found that the NLR is an accurate indicator of infection in these patients. 

Rheumatoid arthritis (RA) is a chronic condition. It is caused by painful inflammation in the joints. RA is treated with drugs that reduce inflammation. They are called disease-modifying anti-rheumatic drugs (DMARDs). RA is also an auto-immune disease. DMARDs work by suppressing the overactive immune system. Increased risk of infection is a side-effect of DMARD treatment. It is important to understand this risk for each DMARD drug. 

Tocilizumab (TCZ) is a biological DMARD (bDMARD). It blocks a chemical called interleukin-6 (IL-6). IL-6 inhibition by TCZ reduces a protein called c-reactive protein (CRP). CRP is an indicator of inflammation. CRP is also an indicator of infection. In patients treated with TCZ, CRP is not a reliable indicator of infection. Recently the neutrophil-to-lymphocyte ratio (NLR) has been suggested as an indicator of infection. Neutrophils and lymphocytes are immune cells found in the blood. It is unclear if the NLR is an accurate indicator in TCZ-treated patients.

This study included 196 patients with RA. All patients were treated with TCZ. The authors investigated reported infections. They compared this to CRP levels and the NLR. NLR before infection (pre-NLR) and during the infection period (post-NLR) was evaluated. 

The post-NLR/pre-NLR ratio was higher in patients with a bacterial infection. A post NLR/pre-NLR cut-off value of 2.25 was an accurate indicator of infection. The sensitivity of NLR as an IOI was 90.5%. This means that 90.5% of patients with a NLR of 2.25 or higher have a bacterial infection. The specificity was 100%. This means that all patients with a NLR lower than 2.25 do not have a bacterial infection. 

The authors concluded that NLR is an accurate indicator of infection in TCZ-treated patients with RA.

This study was based on medical records. Some information such as chronic infections were not considered. Also, the levels of neutrophils and lymphocytes vary in the blood. More studies are needed.