Ratios from full blood count as markers for TB diagnosis, treatment, prognosis: a systematic review

BACKGROUND: The monocyte-to-lymphocyte (MLR) and neutrophil-to-lymphocyte (NLR) ratio are calculated from routine full blood counts. The aim of this study was to systematically review MLR and NLR as biomarkers for diagnosis, treatment response monitoring and prognostic biomarker for TB infection or disease.METHODS: A systematic literature search was conducted in Medline, Embase and the Cochrane Library on 12 January 2022. The following search terms were used: tuberculosis AND (monocyte OR neutrophils), AND lymphocytes AND (diagnostic OR prognostic OR treatment).RESULTS: A total of 2,314 studies were identified, of which 41, covering 11,952 individuals, were included in the final analysis. Studies enrolled a median of 154 individuals (IQR 108-301). Increased MLR and NLR were associated with TB disease when compared to healthy controls and individuals with TB infection. MLR was shown to be prognostic for progression to TB disease and to decrease in response to TB treatment. The cut-offs determined in the studies were highly variable for MLR and NLR, making it impractical to conduct a meta-analysis of sensitivity and specificity.CONCLUSION: Higher MLR and NLR are associated with TB disease and could be used as easy-to-obtain, low-cost additional diagnostic biomarkers. Further studies investigating these biomarkers are needed.