Platelet-to-lymphocyte ratio as a prognostic biomarker for COVID-19 severity: a single center retrospective data analysis and systematic review with meta-analysis of 187 studies

INTRODUCTION: This study aims to evaluate the prognostic value of the platelet-to-lymphocyte ratio in determining the severity and mortality of adults hospitalized for COVID-19 using retrospective data and a meta-analysis of previous studies on the platelet-to-lymphocyte ratio worldwide. MATERIAL AND METHODS: A retrospective study was conducted at the Kırdar City Hospital (Istanbul, Turkey) and included 521 COVID-19 patients. A systematic literature search of EMBASE, MEDLINE, the Cochrane Central Register of Controlled Trials (CENTRAL), and Google Scholar databases was performed for relevant trials relating to the PLR ratio in COVID-19 published before April 12, 2023. RESULTS: In the retrospective part of the study, PLR values were found to predict COVID-19 severity at admission with an AUC of 0.61 (SE = 0.03; 95% CI: 0.56 to 0.65; p = 0.0003) as well as survival status in a statistically significant fashion with an AUC of 0.59 (SE = 0.03; 95% CI: 0.55 to 0.64; p = 0.0004). Results of our meta-analysis showed a significant relationship between PLR and COVID-19 severity, with a pooled standardized mean difference (SMD) of 1.34 (95% CI: 1.13 to 1.55; p < 0 .001), and that PLR was significantly lower among patients who survived compared to deceased patients (SMD = –1.32; 95% CI: 1.57 to –1.07; p < 0.001). CONCLUSIONS: PLR is a valid, readily available marker that can distinguish COVID-19 individuals with distinct progression and survival outcomes.