# The neutrophil‐to‐lymphocyte ratio as a marker of immunosenescence and COVID‐19 outcomes in the elderly: A narrative review

## TL;DR

This review explores how the neutrophil-to-lymphocyte ratio predicts severe COVID-19 outcomes in elderly patients.

## Contribution

The paper highlights NLR as a practical and accessible marker for immune aging and severe COVID-19 in older adults.

## Key findings

- Lymphopenia, neutrophilia, and elevated NLR correlate with worse COVID-19 outcomes in the elderly.
- NLR is a low-cost and reliable indicator of immune dysregulation and mortality risk.
- These markers complement existing research on immunosenescence and provide clinical prognostic value.

## Abstract

Older adults are highly vulnerable to severe COVID‐19. Unlike our previous work on broad immunosenescence, this review focuses on peripheral hematological markers as practical indicators of risk. To examine lymphopenia, neutrophilia, and the neutrophil‐to‐lymphocyte ratio (NLR) as clinically accessible markers of immune aging and COVID‐19 severity in older adults. Literature search of PubMed, Scopus, and Web of Science (up to 2025) for studies on aging, immunosenescence, lymphopenia, neutrophilia, NLR, and COVID‐19. These markers consistently correlate with worse COVID‐19 outcomes; NLR is a simple, reliable indicator of immune dysregulation, systemic inflammation, and mortality risk. Lymphopenia, neutrophilia, and elevated NLR are low‐cost, readily measurable markers associated with COVID‐19 severity, highlighting their prognostic value and complementing prior immunosenescence research.