Table 3.

Summary of findings for association of Rh with susceptibility to the COVID-19 and outcomes

	Reference	Study design	Number of patients	Selection criteria	Limitations	Major outcomes
1	Zietz et al. [24]	A cohort study	N = 14,112	Patients above 18 years old who tested positive for SARS-CoV-2 with known blood types in the New York Presbyterian hospital system	The study mostly focuses on severely-ill patients, so it may not be generalizable to all COVID-19 patients	Rh(−) patients had a 2.7% lower risk of initial infection after adjustment, and also lower risk for both intubation and death
2	Latz et al. [23]	A retrospective multi-institutional study	N = 1289	Patients tested positive for SARS-CoV-2 with a known blood type	Sample size was relatively small and there might be a lead-time bias	Individuals with Rh(−) blood type were less susceptible to infection by SARS-CoV-2
3	Ray et al. [33]	A population-based retrospective cohort study	N = 225,556	People who had ABO blood group assessed between January 2007 and December 2019 and who also had SARS-CoV-2 testing conducted between January 15, 2020, and June 30, 2020, in Ontario, Canada	Patients who died shortly after the infection	B-positive was associated with higher odds of testing positive, whereas O-negative associated with lower infection rate; Rh(+) had higher risk of severe illness or death
4	Taha et al. [35]	A case-control study	N = 557	Individuals surveyed online	Potential exclusion bias due to reliance on the internet for survey completion (i.e., older people may have less access to the internet)	O-positive blood group has the lowest risk of having severe symptoms, and A-positive individuals were the most vulnerable when exposed to the virus