Immature platelets as a biomarker for disease severity and mortality in COVID-19 patients

Background : COVID-19, caused by SARS-CoV-2, is a contagious life-threatening viral disease that has killed more than 2.13M people worldwide. Attempts have been made to identify a biomarker to stratify disease severity to improve resource allocation. Patients with SARS-COV-2 infection manifest with higher inflammatory response and platelet hyperactivity;this raises the question of the role of thrombopoiesis in COVID-19. Immature platelet fraction (IPF%) can be used to assess bone marrow activity, thrombopoiesis. Aims : This study investigates whether the level of thrombopoiesis associates with COVID-19 severity defined by ICU stay, ventilator use, and mortality. Methods : A large cohort of 678 (658, 97% hospitalized) wellcharacterized COVID-19 patients was analyzed. This included 52.4% males, 38.9% White, 26.8% Black, 25.2% Hispanic, 2.5% Asian/AI/ PI, and 6.5% Other. Overall age was 61.5 ± 16.7 years. Other characteristics reviewed included smoking status, comorbidities, and steroid use at the time of admission. Additionally, 5.6% ( n = 38) had thrombosis during admission. Group differences in continuous and categorical variables were tested using Two-sided Wilcoxon rank sum test and Mantel Chi-Square statistics, respectively. Results : Elevated IPF% at presentation was predictive of length of hospitalization ( P < 0.01). Additionally, peak values of IPF% were significantly higher among deceased patients compared to recovered patients (7.9 ± 6.3 vs 5.4 ± 7.8, P < 0.01). Approximately 20% of hospitalized patients were admitted to the intensive care unit (ICU) with an average length of stay 11 ± 12 days;these had significantly higher IPF% at presentation compared to those who did not require ICU care (5.8 ± 4.6 vs 4.7 ± 2.6, P < 0.01). Conclusions : Higher IPF%, as a biomarker of thrombopoiesis, can predict disease severity, length of stay, and mortality risk among hospitalized COVID-19 patients.