Immature Platelets and Platelet Reactivity in Patients with COVID-19

Coronavirus disease 2019 (COVID-19) is associated with a high incidence of thromboembolic events, both venous and arterial. There are currently no specific clinical or laboratory markers to guide antithrombotic therapy for COVID-19 patients. Immature platelets represent a population of hyper-reactive platelets associated with arterial thrombotic events. This prospective study compared consecutive severe COVID-19 patients (n = 53, median age = 73 years) versus patients with sepsis from another origin (n = 41, median age = 69 years). Total platelet counts, immature platelet fraction (IPF) and immature platelet count (IPC) were determined by the Sysmex XN-3000 auto-analyzer on admission and at subsequent time-points. IPC levels three days after admission were significantly higher in the COVID-19 group compared to the sepsis group (13.4 × 10⁹/ L [IQR 9.1-18.5] in the COVID-19 group vs 9 × 10⁹/ L [5.5-14.7] in the sepsis group, P = 0.007). COVID-19 patients with respiratory disease show increased platelet turnover and reactivity, as seen in higher levels of immature platelet indices, especially IPC, compared to the sepsis control group. While these platelet indices remained high, CRP levels decreased, particularly in patients treated with tocilizumab. This reduction in CRP was not accompanied by any apparent clinical improvement. These findings suggest that immature platelets may serve as a biomarker for disease severity in COVID-19 patients and their CRP may not be a reliable marker for disease severity.