Platelet and large platelet ratios are useful in predicting severity of COVID-19

The role of platelets in coronavirus disease (COVID-19) severity requires further exploration. To determine whether the platelet index is useful in predicting COVID-19 severity, we compared the platelet index in patients with higher and lower oxygen requirements (≥ 4 L/min vs. < 4 L/min) and patients without COVID-19. We also analyzed the time course of the platelet index in each group. A total of 285 patients with COVID-19 and 36 without COVID-19 who were hospitalized at Fussa Hospital were analyzed. After matching for oxygen requirement at admission, multivariate analysis was performed. Platelets (≤ 16.6 × 10⁴/μL) and platelet-large cell ratio (P-LCR) (≥ 27.8%) were significant factors influencing severity. Based on these factors, we created the Fussa platelet score, and the group with a Fussa platelet score ≥ 2 was significantly more likely to reach the 4 L/min oxygen requirement (event-free survival: Fussa platelet score ≥ 2 versus < 2, P < 0.00000001). Analysis of platelet index by time period showed a significant increase from 6-10 days after onset. The Fussa platelet score can be measured quickly, easily, and inexpensively in a clinic and may be useful in determining need for transfer to a critical care hospital.