Hematological Biomarkers in COVID-19 Severity Assessment
Summary
Hematological biomarkers have emerged as accessible and cost-effective tools for stratifying risk in patients with COVID-19. Routine blood counts provide insight into the host inflammatory response, with neutrophilia and lymphopenia serving as hallmarks of severe disease. Composite indices such as the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and systemic inflammation index (SII) integrate these cellular changes to yield stronger prognostic signals than isolated parameters. Dynamic monitoring of these ratios can identify early deterioration, guide triage decisions and optimise allocation of critical care resources. Across diverse populations, elevated NLR and related indices have been linked to higher likelihood of intensive care admission, mechanical ventilation and in-hospital mortality. As global health systems continue to grapple with emerging SARS-CoV-2 variants and uneven vaccine coverage, reliable bedside biomarkers remain essential for personalised management and rapid escalation of therapy in high-risk individuals.
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Hematological Biomarkers in COVID-19 Severity Assessment publication trend
The graph below shows the total number of articles in hematological biomarkers in covid-19 severity assessment across all publications each year (not limited to Nature Index journals).
Technical terms
Neutrophil-to-lymphocyte ratio (NLR): Ratio of absolute neutrophil count to absolute lymphocyte count, indicating balance between innate and adaptive immunity.
Platelet-to-lymphocyte ratio (PLR): Ratio of platelet count to lymphocyte count, reflecting inflammatory and thrombotic interplay.
Systemic inflammation index (SII): Composite measure calculated as neutrophils × platelets / lymphocytes, quantifying overall inflammatory burden.
Derived neutrophil-to-lymphocyte ratio (dNLR): Variation of NLR computed as neutrophils divided by the difference between total white cells and neutrophils, adjusting for lymphopenia.
Systemic inflammation response index (SIRI): Index combining neutrophil, monocyte and lymphocyte counts (neutrophils × monocytes / lymphocytes) to assess inflammatory response intensity.
References
- Systemic inflammation index, disease severity, and mortality in patients with COVID-19: a systematic review and meta-analysis. Frontiers in Immunology (2023).
- Predictive values of neutrophil-to-lymphocyte ratio on disease severity and mortality in COVID-19 patients: a systematic review and meta-analysis. Critical Care (2020).
- Novel Systemic Inflammation Markers to Predict COVID-19 Prognosis. Frontiers in Immunology (2021).
- The Predictive Role of NLR, d-NLR, MLR, and SIRI in COVID-19 Mortality. Diagnostics (2022).
- Neutrophil-to-Lymphocyte Ratio (NLR) Is a Promising Predictor of Mortality and Admission to Intensive Care Unit of COVID-19 Patients. Journal of Clinical Medicine (2022).
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