To the Editor,
Recently, Dr. Lee et al.[1] examine the association between neutrophil to lymphocyte (NLR)/platelet to lymphocyte (PLR) and in-hospital mortality in patients with trauma. They found that low NLR and PLR were associated with increased in-hospital mortality rates. This study is well designed. However, several issues should be noted. As the reviewer indicated, the current finding is different from most previous studies which reported that high NLR[2–4] or PLR[5,6] is a significant risk factor for poor prognosis in various cohorts, such as critically ill trauma,[2,3] traumatic brain injury,[4] cardiac diseases,[5] and tumor.[6] The reason for these contradictory findings remains unclear. The authors speculated that some factors may contribute to the inconsistent findings, such as different inclusion criteria (patients who died within the first 24 h were included in the study), different time intervals from injury to arrival, and severity of trauma.
We are concerned that there are may be other reasons. As common blood parameters, both platelet and neutrophil count have normal ranges, and according to clinical experience,[7] both extremely low and high neutrophil and platelet count, which to a certain degree reflected the value of NLR and PLR, are associated with poor outcomes. In addition, several studies have indicated that PLR and NLR showed a non-linear predictive ability that both high and low PLR[8] or NLR[9,10] were associated with increased mortality in different cohorts. Therefore, the association between NLR/PLR and in-hospital mortality in trauma patients may also be non-linear. When we directly included these indexes in a generalized linear model (including logistic model), we assumed that there was a linear relationship between NLR/PLR and the dependent outcomes. Therefore, the results would be severely biased by the proportion of patients with high or low NLR/PLR. This could also account for these inconsistent findings. Multivariate models with restricted cubic splines or polynomial regression may be optimal options to solve this limitation. Finally, we thank Dr. Lee for their valuable research.
Footnotes
Peer-review: Internally peer-reviewed.
Authorship Contributions: Concept: F.C.; Supervision: F.C.; Analysis: Y.S.; Literature search: Y.S.; Writing: F.C.; Critical revision: Y.S.
Conflict of Interest: None declared.
Financial Disclosure: The authors declared that this study has received no financial support.
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