Validation of neutrophil-to-albumin ratio in discriminating infection from disease activity among systemic lupus erythematosus patients

Background and objectives: The Neutrophil/albumin ratio (NAR) has emerged as a novel biomarker in inflammatory conditions. This work aimed to assess the role of the neutrophil/albumin ratio in the differentiation between systemic lupus erythematosus (SLE) activity and infection in lupus patients. Methods: A cross-sectional study was conducted on SLE patients classified into two groups according to the evidence of infection: 36 non-infected lupus patients and 53 infected lupus patients at the Rheumatology and Rehabilitation Department. The Neutrophil/albumin ratio (NAR), erythrocyte sedimentation rate/C-reactive protein ratio (ESR/CRP), neutrophil/lymphocyte ratio (NLR), Systemic Lupus Erythematosus Disease Activity Index (SLEDAI-2K), and evidence of bacterial infection were detected in both groups. Results: NAR had significant positive correlations with other parameters of infections, including procalcitonin levels (r = +0.73, P≤0.001) and NLR (r = +0.582, P≤0.001). Additionally, there was a significant negative correlation between NAR and ESR/CRP ratio (r = -0.450, P≤0.001); however, the correlation between NAR and SLEDAI was very weak (r = +0.080, P=0.455). NAR at a cut-off of 110.85 and 95% CI was 96.2% sensitive, 80.6% specific, and 89.9% accurate for the detection of infection among SLE patients; however, at the same cut-off, it was 70.9% sensitive, 44.1% specific, and 60.7% accurate for prediction of flare among SLE patients. Conclusion: NAR is a rapid, feasible, affordable, and valid test for detecting infection in SLE patients. It has 96.2% sensitivity, 80.6% specificity, and 89.9% accuracy, which would be valuable in distinguishing infection from flare-up in SLE.