Table 3.

Summary of key study limitations.

First author	Limitations
Ray [21]	Inability to test patients who died quickly due to critical illness
Zhao [22]	Moderate sample size (n = 2,173), single ethnic group
Li [20]	Moderate sample size (n = 2,153), single ethnic group, no covariate adjustment, potential subject overlap with Zhao [22]
Hoiland [17]	Very small sample size (n = 95), limited to ICU subpopulation, blood group data missing in 25% of ICU-admitted patients
Leaf [19]	Moderate sample size (n = 2,033), blood group data missing in one-third of subjects
Latz [18]	Moderate sample size (n = 1,289), lead time bias
Zietz [23]	Selection bias for inpatient hospital population due to limited testing
Barnkob [43]	ABO data available for only 62% of tested individuals, female sex overrepresented at 71% of negative and 67% of positive subjects
Boudin [45]	Moderate sample size (n = 1,279), very high infection rate (76%), subjects not representative of general population (ie, young, healthy)

Abbreviation: ICU = intensive care unit.