Platelet-to-lymphocyte ratio (PLR), a novel biomarker to predict the severity of COVID-19 patients: a systematic review and meta-analysis

Background Platelet-to-lymphocyte ratio (PLR), a novel inflammatory marker, has been suggested to be able to predict the severity of COVID-19 patients. This systematic review aims to evaluate the association between PLR levels on admission and the severity of COVID-19 patients. Methods A systematic literature search was done on 23 July 2020 to identify peer-reviewed studies across four different databases (Ovid MEDLINE, EMBASE, SCOPUS, and the Cochrane Library), preprints from two databases (MedRxiv and SSRN), and grey literature from two databases (WHO COVID-19 Global Research Database and Center for Disease Control and Prevention COVID-19 Research Article). Research articles comparing the PLR value on admission in adult patients with COVID-19 with varying degrees of severity were included in the analysis. The following keywords were used for the search: 9COVID-199, 9PLR9, 9severity9, and 9mortality9. The inverse variance method was used to calculate the pooled effect standardized mean difference (SMD) along with its 95% confidence interval (CI). Results A total of seven studies were included in the meta-analysis, six of which were conducted in China. From a total of 998 participants included, 316 (31.7%) had severe diseases; and those in the severe group were generally older and had underlying diseases compared to the non-severe group. In comparison to non-severe patients, the meta-analysis showed that severe COVID-19 patients had higher PLR levels on admission (SMD 0.68; 95%CI 0.43-0.93; I2 =58%). Conclusion High PLR levels on admission were associated with severe COVID-19 cases. Therefore, on-admission PLR level is a novel, cost-effective, and readily available biomarker with a promising prognostic role for determining the severity of COVID-19 patients.