# Clinical applications of blood cell ratios in veterinary hematology: From diagnosis to prognosis

## TL;DR

This review explores how blood cell ratios help diagnose and monitor diseases in animals, highlighting their usefulness and future potential.

## Contribution

The paper systematically categorizes and evaluates current veterinary hematological ratio studies to guide future research and standardization.

## Key findings

- Neutrophil-to-lymphocyte ratio (NLR) is widely used for diagnosing and predicting disease outcomes in animals.
- Platelet-based ratios and distribution widths are gaining attention for their role in predicting disease severity.
- Blood cell ratios are valuable for monitoring and staging various inflammatory and immune-related conditions in veterinary patients.

## Abstract

When examining routine blood tests, hematological ratios can demonstrate the systemic impact caused by diseases. Hematological ratios are less susceptible to interference than individual parameters.

For a better understanding of these ratios, they must be collected and analyzed together in a comprehensive method. This review aims to categorize and discuss current hematological ratio studies in veterinary medicine, emphasize their potential, and identify future research needs.

Studies investigating blood cell ratios in veterinary medicine were comprehensively searched in the literature utilizing PubMed, Web of Science, and Scopus databases, incorporating a variety of key words. All studies in which blood cell ratios were used in veterinary patients for diagnostic, prognostic, or monitoring purposes were included. Observational studies, retrospective studies, and experimental models were all combined in this review.

Neutrophil-to-lymphocyte ratio (NLR) is the most widely used ratio for diagnosing and prognosticating inflammatory, infectious, endocrine, cardiovascular, and neoplastic diseases in animals. The monocyte-to-lymphocyte ratio (MLR) and lymphocyte-to-monocyte ratio (LMR) are also relevant for immune-mediated, gastrointestinal, and neoplastic conditions. Animals have also been analyzed using ratios based on platelets (like the platelet-to-lymphocyte ratio (PLR) and red blood cells. Interest in the use of red cell distribution width (RDW) and platelet distribution width (PDW) in calculations has grown. When platelet activity and leukocyte responses are integrated into composite indices, they improve the prediction of disease severity.

In veterinary medicine, these ratios are useful for detecting, monitoring, staging, and prognosing inflammatory conditions, including tumors, infections, autoimmune disorders, cardiovascular disease, and so on. The goal should be to minimize inconsistencies regarding the application of these ratios in the future while establishing a comprehensive standard framework.