Neutrophil-to-Lymphocyte Ratio as a Biomarker in Erythema Nodosum Leprosum: A Systematic Review and Meta-Analysis

Objectives Erythema nodosum leprosum (ENL) is a severe type 2 leprosy reaction causing recurrent episodes, nerve damage, and disability. Diagnosis still relies on clinical assessment and tests often unavailable in resource-limited settings. The neutrophil-to-lymphocyte ratio (NLR), derived from routine complete blood counts, has been proposed as a low-cost inflammatory biomarker. This systematic review and meta-analysis aimed to assess differences in NLR between ENL and non-reactional leprosy. Methods Following PRISMA 2020 and a PECO framework, we searched PubMed, ScienceDirect, Scopus, and Google Scholar up to 20 November 2025 for observational studies reporting NLR in ENL versus non-reactional leprosy. Quality was assessed using the Newcastle–Ottawa Scale. Pooled mean differences were estimated using a fixed-effect model in RevMan 5.4.1, with heterogeneity evaluated by Cochran's Q and the I 2 statistic. Results Of 677 records, five observational studies (162 ENL and 423 non-reactional leprosy patients) met the inclusion criteria. NLR was higher in ENL, with a pooled mean difference of 5.79 (95% CI 4.58–6.99; I 2 = 56%; P < 0.00001). Conclusions NLR is markedly elevated in ENL compared with non-reactional leprosy, supporting its potential as a simple, low-cost biomarker. Prospective studies are needed to define optimal cut-off values for routine use.