4C Mortality Score = sum of the points for eight variables (0–21 points).

Variable	Finding	Points
Age	<50 years	0
	50–59 years	2
	60–69 years	4
	70–79 years	6
	≥80 years	7
Sex at birth	Male	1
Relevant comorbidities	1	1
Relevant comorbidities	≥2	2
Respiratory rate	20–29 breaths/min	1
Respiratory rate	≥30 breaths/min	2
Peripheral oxygen saturation on room air	<92%	2
Glasgow Coma Scale	<15	2
Urea	7–14 mmol/L (BUN 19.6–39.2 mg/dL)	1
Urea	>14 mmol/L (BUN >39.2 mg/dL)	3
C-reactive protein	50–99 mg/L	1
C-reactive protein	≥100 mg/L	2

Total	Risk category	Observed in-hospital mortality in the validation cohort
0–3	Low	1.2%
4–8	Intermediate	9.9%
9–14	High	31.4%
15–21	Very high	61.5%

4C Mortality Score for COVID-19