A Low Lymphocyte: Monocyte Ratio Provides A Clue To Diagnosing Early Dengue Fever

Highlights • Peripheral blood leucocyte ratios are useful infection biomarkers. • Neutrophil:lymphocyte ratio (NLR) is predictive of bacteraemia. • NLR should be included in future stratification models to identify sepsis endotypes. • Lymphocyte:monocyte ratio is predictive of influenza virus infection. • Utility was also found in CAP, UTI, pertussis, CCHF and diabetic foot infections.
Summary Objectives To assess the utility of the neutrophil:lymphocyte (NLR), lymphocyte:monocyte (LMR) and platelet:lymphocyte ratios (PLR) as infection biomarkers. Methods PubMed/MEDLINE, Embase and Cochrane databases were searched to identify eligible articles. Studies of diagnosis, severity or outcome were included. PROSPERO systematic review registration CRD42017075032. Results Forty studies were included, reporting on bacterial and viral infections, malaria, and critical illness due to sepsis. Ten studies reported an association of higher NLR with bacteraemia, supported by meta-analysis of patient-level data (five studies, n = 3320; AUC 0.72, p12.65. Two studies reported an association with lower LMR and diagnosis of influenza virus infection in patients with respiratory tract infection. Meta-analysis of patient-level data (n = 85; AUC 0.66, p = 0.01) identified a cut-off of ≤2.06. The directionality of associations between NLR and outcomes in heterogeneous cohorts of critically ill adults with sepsis varied. Potential clinical utility was also demonstrated in pneumonia (NLR), pertussis (NLR), urinary tract infection (NLR), diabetic foot infections (NLR) and Crimean Congo Haemorrhagic Fever (PLR). Longitudinal measurement of LMR during respiratory virus infection reflected symptoms and NLR during sepsis and bacteraemia predicted mortality. Conclusions Peripheral blood leucocyte ratios are useful infection biomarkers, with the most evidence related to diagnosis of bacteraemia and influenza virus infection. In critical illness due to sepsis, a signal towards an association with NLR and outcomes exists, and NLR should be evaluated in future stratification models. Longitudinal measurement of ratios during infection could be informative. Overall, these biomarkers warrant further recognition and study in infectious diseases.