In the Literature
Doulidis PG, Vali Y, Frizzo Ramos C, Guija-de-Arespacochaga A. Retrospective evaluation of the neutrophil-to-lymphocyte ratio as a prognostic marker in cats with blunt trauma (2018-2021): 177 cases. J Vet Emerg Crit Care (San Antonio). 2024;34(5):478-486. doi:10.1111/vec.13414
The Research …
Neutrophil:lymphocyte ratio (NLR) may be an important marker of dysregulation of the pro- and anti-inflammatory response balance in the hours following trauma and has been associated with mortality in humans. NLR has also been examined in veterinary patients with nontraumatic diseases, including infectious, inflammatory, and endocrine diseases, as well as neoplasia.1-4
This retrospective study examined NLR as a potential prognostic marker for blunt trauma in 177 cats presented to a university clinic. CBC performed within 24 hours of trauma and posttrauma thoracic radiography were required for inclusion in the study. Examined parameters included patient history, physical examination findings, need for intensive care and oxygen support, outcome, and animal trauma triage (ATT) score, which was classified as mild (1-3), moderate (4-7), or severe (>8). Of the cats with blunt trauma, 42% had high-rise syndrome, 12% were hit by a car, and 46% had trauma of unknown origin; 10% of the cats died or were euthanized. Forty-eight healthy cats were included as controls.
Neutrophil counts were significantly higher and lymphocyte counts were significantly lower in the trauma group compared with the control group, resulting in significantly higher median NLR in cats with trauma (8.4 versus 2.3). The NLR cutoff value with the highest sensitivity (74%) and specificity (71%) for distinguishing cats with trauma from healthy cats was 4.45. A higher median NLR was found in cats with thoracic trauma (9.2) than injured cats without thoracic trauma (6.4). No difference in NLR was identified for cats that required longer hospitalization or intensive care; however, NLR differed among the 3 ATT score groups: cats with mild scores had a median NLR of 3.98, cats with moderate scores had a median NLR of 13.1, and cats with severe scores had a median NLR of 28.2. No difference in NLR was noted between survivors and nonsurvivors, but outcome data may have been difficult to interpret because of the low number of nonsurvivors.
The authors advised caution with machine leukocyte counts, as bands (immature neutrophils) may be counted as lymphocytes, which could lead to errors in NLR. Manual differential counts should be used, particularly when values outside the reference interval are identified.
… The Takeaways
Key pearls to put into practice:
NLR of 4.45 had 74% specificity and 71% sensitivity for differentiation of cats with blunt trauma and healthy cats.
Presence of thoracic trauma was associated with a significantly higher NLR; cats with thoracic trauma had a median NLR of 9.2, compared with 6.4 in injured cats without thoracic trauma.
NLR was not associated with survival but correlated well with grouped ATT scores. Cats with higher ATT scores had higher NLR.
Manual differential counts should be performed to help identify machine misreads, especially when scatterplots appear poorly distributed.
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