In this study, blood type ‘O’ was the most dominant types followed by ‘A’, ‘B’ and ‘AB’. Nationwide ABO-Rh(D) blood group data is lacking in Ethiopia. Mason and colleagues, perhaps in a first attempt, screened 878 Ethiopian soldiers who were participating in the Korean War in the late 1940s and found ‘O’, ‘A’, ‘B’ and ‘AB’ to be 41.2, 28.5, 24.0 and 6.3%, respectively . In the 1960s it was reported that type ‘A’ frequencies were about 20% and ‘B’ 16% in Tigre, Amhara and other population groups in the country .
Probably the only published study from Ethiopia that used relatively large sample size (164,380) was that of Seifu and Dagne some 30 years back . That study extracted several years hospital and red cross data and found the frequencies of ‘O’, ‘A’, ‘B’ and ‘AB’ to vary from 40–54, 25–31, 17–25 and 2–8% respectively. The donors were from northern, western and central parts of the country including Addis Ababa, the capital. Later fragmented and small-scale studies from different parts of the country reported comparable results [20,21,22].
In this study, while type ‘O’ was dominant overall and among the Nilotic natives of Gambella, type ‘A’ had a significantly higher frequency among the ‘highlanders’ who belong to different ethnic groups. Blood type ‘O’ is 50% and higher reaching even 100% in some isolated populations . The proportion of patients devoid of the D-antigen (Rh factor) was substantial (19.37%) compared to both national and global data. About 89–95% donors all over the world are detected as Rh positive. Mason and colleagues detected 37 (4.2%) Rh negatives among 878 Ethiopian soldiers during the Korean War . The proportion of Rh factor negatives ranged from 1–7% in more representative report from Ethiopia . In a recent small-scale study in south-central Ethiopia the proportion of Rh negative subjects ranged from 9–8% .
The frequency of the Rh-negative phenotype differs significantly between populations. In Africa and Asia the Rh-negative phenotype is less common. For example, there are reports of a 6% rate of Rh-negatives in Nigeria  and only 1% in Madagascar . In various regions of India Rh negativity was found to be 0.6–8.4% . In South East Asia and Far East the D-negative phenotype is even rarer. In China [27, 28], Indonesia , and Japan  less than 1% of the population is Rh-negative.
On the other hand, Western nations like Britain  and United States  have Rh factor negativity of 17 and 15%, respectively, which are closer to the findings of this study. A study in one region of Saudi Arabia revealed that 29% of the population was Rh negative . Rh-negative frequencies of about 29% were documented among Basques and in distinct populations living in the High Atlas Range of Morocco , which have the highest reported prevalence of Rh-negative phenotypes apart from that from Saudi Arabia above.
The higher frequency of group ‘O’ than non-‘O’ phenotypes among the Nilotic natives in this study agrees with the hypothesis that in malaria endemic areas type ‘O’ is dominant. The Nilotic people are natives to the study area which is among the highest year-round malaria transmission areas in Ethiopia. It appears that the natives with blood type ‘O’ better survived severe malaria. On the other hand, both Rh-negative and ‘O’ phenotypes might have encouraged malaria transmission in the area as asymptomatic carriers prevailed probably because of their resistance to malarial disease showing the beneficial effects of the phenotypes.
As aforementioned, in Africa Rh negativity is very low (1–3%) with the exception of the Yorubas, Chad or Cameroon areas . Previous reports for Ethiopia showed that the Rh negativity in the country to be three times that of the continental average.
The current data calls for routine screening of pregnant women to avoid the potential risk of erythroblastosis fetalis in the study area. In fact both women and men are required to be tested before having a child. But this is rarely practiced in Ethiopia and the current finding would be helpful in creating awareness. Moreover, since Rh-negative blood group is rare in many populations it is scarcely available in blood banks. The finding shows that Rh-negative group is more common than expected among certain groups and such individuals may be approached, encouraged and convinced to donate blood to make this blood group more available in blood banks for the needy and better save life.