Neutrophil-to-lymphocyte ratio may be a valuable biomarker to aid clinicians in identifying patients with severe COVID-19 and moderate to severe acute respiratory distress syndrome (ARDS), according to a research letter published in Critical Care. This finding has assisted clinicians in providing effective respiratory support strategies and finding moderate to severe ARDS patients at high indication for veno-venous extracorporeal membrane oxygenation.

This trial (Chinese Clinical Trial Registry, ChiCTR2000029758) included patients diagnosed with severe COVID-19 from 21 hospitals in Sichuan Province in China between January 16 and March 15, 2020. The maximum values of neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, procalcitonin, and C-reactive protein during the first 3 days after being diagnosed with severe COVID-19 were included in the analysis. Multivariate logistic regression analysis and the area under the receiver operating characteristic (ROC) curve were used to analyze the ability of neutrophil-to-lymphocyte ratio in predicting ARDS.

In total, 81 patients were defined as having severe COVID-19; 44 of these patients were diagnosed with ARDS. The area under the ROC curve for neutrophil-to-lymphocyte ratio was 0.71, and was 0.591, 0.494, and 0.625 for platelet-to-lymphocyte ratio, procalcitonin, and C-reactive protein, respectively. Patients were then divided into 2 groups based on the median as a cutoff value. In the high neutrophil-to-lymphocyte ratio group (ratio > 9.8), patients showed a higher incidence of ARDS (P = .005) and higher rate of noninvasive (P = .002) and invasive (P = .048) mechanical ventilation.

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Investigators further defined moderate to severe ARDS as patients with ARDS with an oxygenation index less than 150. The area under the ROC curve for these moderate to severe patients with ARDS was 0.749, 0.660, 0.531, and 0.635 for neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, procalcitonin, and C-reactive protein, respectively. The neutrophil-to-lymphocyte ratio cutoff value for moderate to severe ARDS was 11.

“[Neutrophil-to-lymphocyte ratio] is an extremely common laboratory test wherein the initial [neutrophil-to-lymphocyte ratio] value can be used to identify high-risk patients with moderate to severe ARDS, with the optimal threshold value of 11,” the researchers wrote.

According to investigators, this biomarker might be useful in determining allocations of respiratory equipment among patients in the intensive care unit, as well as for the early assessment of extracorporeal membrane oxygenation. They do caution, however, that further clinical studies are needed to evaluate the benefits of neutrophil-to-lymphocyte ratio in ARDS.


Ma A, Cheng J, Yang J, Dong M, Liao X, Kang Y. Neutrophil-to-lymphocyte ratio as a predictive biomarker for moderate-severe ARDS in severe COVID-19 patients. Crit Care. 2020;24(1):288.

This article originally appeared on Infectious Disease Advisor