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. 2023 Jun;12(6):1625-1640.
doi: 10.1007/s40121-023-00813-1. Epub 2023 May 17.

Dynamic NLR and PLR in Predicting COVID-19 Severity: A Retrospective Cohort Study

Erika Asperges #  1 , Giuseppe Albi #  2 , Valentina Zuccaro  1 , Margherita Sambo  1   3 , Teresa C Pieri  1   3 , Matteo Calia  1   3 , Marta Colaneri  1 , Laura Maiocchi  1 , Federica Melazzini  4 , Angioletta Lasagna  5 , Andrea Peri  6 , Francesco Mojoli  7 , Paolo Sacchi  1 , Raffaele Bruno  8   9
Affiliations

Dynamic NLR and PLR in Predicting COVID-19 Severity: A Retrospective Cohort Study

Erika Asperges et al. Infect Dis Ther. 2023 Jun.

Abstract

Introduction: The hyperinflammation phase of severe SARS-CoV-2 is characterised by complete blood count alterations. In this context, the neutrophil-to-lymphocyte ratio (NLR) and the platelet-to-lymphocyte ratio (PLR) can be used as prognostic factors. We studied NLR and PLR trends at different timepoints and computed optimal cutoffs to predict four outcomes: use of continuous positive airways pressure (CPAP), intensive care unit (ICU) admission, invasive ventilation and death.

Methods: We retrospectively included all adult patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia admitted from 23 January 2020 to 18 May 2021. Analyses included non-parametric tests to study the ability of NLR and PLR to distinguish the patients' outcomes at each timepoint. Receiver operating characteristic (ROC) curves were built for NLR and PLR at each timepoint (minus discharge) to identify cutoffs to distinguish severe and non-severe disease. Their statistical significance was assessed with the chi-square test. Collection of data under the SMACORE database was approved with protocol number 20200046877.

Results: We included 2169 patients. NLR and PLR were higher in severe coronavirus disease 2019 (COVID-19). Both ratios were able to distinguish the outcomes at each timepoint. For NLR, the areas under the receiver operating characteristic curve (AUROC) ranged between 0.59 and 0.81, and for PLR between 0.53 and 0.67. From each ROC curve we computed an optimal cutoff value.

Conclusion: NLR and PLR cutoffs are able to distinguish severity grades and mortality at different timepoints during the course of disease, and, as such, they allow a tailored approach. Future prospects include validating our cutoffs in a prospective cohort and comparing their performance against other COVID-19 scores.

Keywords: COVID-19; Cutoff; ICU; Mortality; NLR; PLR.

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Conflict of interest statement

The authors Erika Asperges, Giuseppe Albi, Valentina Zuccaro, Margherita Sambo, Teresa C Pieri, Matteo Calia, Marta Colaneri, Laura Maiocchi, Federica Melazzini, Angioletta Lasagna, Andrea Peri, Francesco Mojoli, Paolo Sacchi and Raffaele Bruno have nothing to disclose.

Figures

Fig. 1
Fig. 1
Pyramid plot of age and gender of the study population. At the extremes (≤ 39 and ≥ 85 years) patients are prevalently females, while in the middle, which constitutes the majority of admissions, they are prevalently male
Fig. 2
Fig. 2
Histogram showing the distribution of patients’ length of stay (LOS), reported in days. The mean LOS was 12 ± 13 days, and the maximum was 141 days
Fig. 3
Fig. 3
Neutrophil (A), platelet (B) and lymphocyte (C) mean trends (with 95% confidence interval) from the total population are presented in grey with a dashed line; the blue and red lines represent the mean trend for male and female patients, respectively
Fig. 4
Fig. 4
Ratio trends at the four timepoints. NLR (A) and PLR (B) mean trends (with 95% confidence intervals) from the total population are presented in grey with a dashed line; the blue and red lines represent the mean trend for male and female patients, respectively. NLR, neutrophil-to-lymphocyte ratio; PLR, platelet-to-lymphocyte ratio
Fig. 5
Fig. 5
Ratio trends for each outcome at the four timepoints. NLR (A) and PLR (B) mean trends (with 95% confidence intervals) are in orange for the patients with the outcome and in blue for the patients without the outcome. P values are reported for each outcome and express the significance of the difference in the NLR or PLR values for each timepoint (Mann–Whitney test). NLR, neutrophil-to-lymphocyte ratio; PLR, platelet-to-lymphocyte ratio
Fig. 6
Fig. 6
NLR cutoff values for males and females, plotted in order of timepoint and severity. NLR, neutrophil-to-lymphocyte ratio
Fig. 7
Fig. 7
PLR cutoff values for males and females, plotted in order of timepoint and severity. PLR, platelet-to-lymphocyte ratio
Fig. 8
Fig. 8
ROC curves for NLR (A) and PLR (B) cutoffs’ ability at predicting each outcome at admission, 48 h and 7 days. AUROCs are reported in the legends
Fig. 9
Fig. 9
Comparison of NLR (blue) and PLR (orange) ROC curves for each outcome at each timepoint performed with DeLong’s test. P value is considered significant if < 0.05. Results are truncated to < 0.001 if lower than this value. NLR: Neutrophil to Lymphocyte Ratio; PLR: Platelet to Lymphocyte Ratio
See this image and copyright information in PMC

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