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Abstract
Objectives ABO and Rh blood group systems are the major factors affecting the blood transfusion safety. The frequency and distribution of these blood group systems vary worldwide. We aimed to determine the frequency and distribution of ABO and Rh blood group systems among first-time blood donors at the Northern Zone Blood Transfusion Center in Kilimanjaro, Tanzania.
Design Cross-sectional descriptive population-based study.
Setting Data on ABO and Rh blood group systems were obtained and analysed from the Northern Zone Blood Transfusion Center among first-time blood donors.
Participants There were 65 535 first-time blood donors aged 15–55 years who donated at the Northern Zone Blood Transfusion Center from January 2017 to December 2019.
Outcome measures The percentage of ABO and Rh blood group systems among different categories of blood donors was calculated.
Results Retrospective data from Blood Establishment Computer System of 65 535 first-time blood donors were analysed in the present study. The mean age of the blood donors was 30.6±11.2 years (range: 15–55 years). The vast majority of the blood donors 84.2% (n=55 210) were men. Also, the majority 69.6% (n=45 595) were aged ≥35 years. Blood group O was the most common blood group which was found in over half 52.4% (n=34 333) of the blood donors and majority 95.3% (n=62 461) of the donors were Rh positive. Moreover, the majority 78.3% (n=51 336) were voluntary donors and the remaining 21.7% (n=14 199) were replacement donors.
Conclusion Majority of the donors had blood group O and also the vast majority of the donors were Rh positive. Considering the large size of our study population, this has provided a more comprehensive information regarding the frequency and patterns of ABO and Rh blood group systems in Tanzania. The observed association of blood group A with one of the regions from which donors were coming from, is intriguing and further studies may confirm possible related genetic evolution.
- HAEMATOLOGY
- Blood bank & transfusion medicine
- Blood bank & transfusion medicine
- Ophthalmology
- Hepatobiliary surgery
- Colorectal surgery
Data availability statement
Data are available upon reasonable request. Data that were used in this study are available on reasonable request from the manager of the blood bank using email: northernzonebtc@org.tz
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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- HAEMATOLOGY
- Blood bank & transfusion medicine
- Blood bank & transfusion medicine
- Ophthalmology
- Hepatobiliary surgery
- Colorectal surgery
Strengths and limitations of this study
To our knowledge, this is the largest population-based study of ABO and Rh blood group systems on frequency and distribution in different regions of the general Tanzanian population.
This study exclusively included first-time blood donors which is important for sustainability of the willingness to donate blood among individuals in the country.
The major limitation of this study is that we did not further investigate the subtypes of the ABO blood groups such as A1, A2, A3, Aw, Ax and Ael.
The fact that data were collected from a single zonal centre in the country, this affected the generalisability of our findings.
Introduction
The ABO blood group system is used to characterise the ABO blood groups by the presence of A, B or AB antigens.1 The blood groups are identified depending on the expression of specific carbohydrate sugars on the surface of red blood cells such as N-acetylgalactosamine and D-galactose for A and B antigen, respectively.2 These sugars are structured on the H antigen in which blood group O is formed when the H antigen remains unchanged.2 The Rh blood group system is the most polymorphic of the human blood groups and it comprises not less than 45 independent antigens which are more of clinical significance in transfusion medicine.3 The phenotypes of Rh blood group system are encoded by two distinct genes which carry C or c together with either E or e antigens, and the D antigen have been elucidated.4 The distribution of Rh positive and Rh negative groups vary between countries globally, where, for example, in Britain and USA the frequency of Rh negative group is relatively higher than other regions.5
There is limited data regarding assessment of the frequency and distribution of the ABO and Rh blood group systems in the practice of transfusion medicine in Tanzania. Additionally, there is a shortage of blood from the blood banks in Tanzania. The need for knowledge of frequency and distribution of the ABO and Rh blood group systems is mandatory for effective management of blood bank centres at all levels in Tanzania. Therefore, investigating the frequency and distribution of the different blood groups among blood donors in the country is of paramount importance for quick and safe blood transfusion practices.6 Knowing the frequency of these two important blood group systems in a Tanzanian population is important for blood banks and transfusion centres to address blood safety and product usage requirements.7
In this study, we aimed to assess the frequency and distribution of ABO and Rh blood groups from the Northern Zone Blood Transfusion Center (NZBTC) in Kilimanjaro, Tanzania, among first-time blood donors from 2017 to 2019.
Materials and methods
Study design
A retrospective cross-sectional and descriptive study was conducted so as to investigate the patterns of ABO and Rh blood groups among first-time blood donors.
Study setting and period
This study was carried out at NZBTC which is situated in Moshi municipality within Kilimanjaro region. The study included retrospective data from the Blood Establishment Computer System (BECS) of first-time blood donors from January 2017 to December 2019. The Moshi municipality is found in the Northern area of Tanzania, 462 km away from the economic capital city of Tanzania (Dar es Salaam) and 387 km to the national capital of Tanzania (Dodoma). The current total population of the zone is estimated as 184 292. NZBTC blood bank was established in 2004 through cooperative agreement of the USA and government of Tanzania by support of President’s Emergency Plan for AIDS Relief funding. At present, the blood bank provides blood for all hospitals in the whole of Northern zone which encompasses Kilimanjaro, Tanga and Arusha regions. The blood bank also serves neighbouring regions such as Manyara.
Study population
A total of 65 535 first-time blood donors without deferral characteristics and with complete clinical data and information on ABO and Rh blood group systems were included in the study. Data regarding age, sex, place of residence and type of blood group systems were retrospectively extracted from the BECS.
Recruitment of the blood donors
All individuals visiting the blood bank centre for the intention of donating blood are first registered and then counselled by the trained donor counsellors. This is followed by assessment of the eligibility for blood donation using local guidelines.
Blood grouping procedure
ABO and Rh blood group systems were determined using tube method as per manufacturer’s instructions.8
Data collection procedure
Extraction of the required data from the BECS at the blood bank centre was done by a data manager. The extracted data included age, sex, type of blood donor, frequency of blood donation, region of the donor and year of donation. The extracted data were then entered in Excel spreadsheet.
Statistical analysis
The collected data were exported from the Excel spreadsheet to the Statistical Package for Social Science (SPSS) programme V.21.0 (IBM SPSS pack, Chicago, USA) programme. This was followed by cleaning for errors which was done by running frequency and crosstabs. Age was summarised as mean±SD while categorical data (sex, type of blood donor and Rh status) were summarised in proportions. Χ2 statistical test was used to determine the association between categorical variables. P value was considered to be significant when it was less than 0.05.
Patient and public involvement statement
This work did not include direct interaction with patients or the public in designing and conceptualisation of this work.
Results
Selection process of the cases to be included in the present study
The process of recruiting the donors in the study is outlined in figure 1. A total of 69 663 blood donors were recorded at the blood bank for the period of 3 years (2017–2019). Of all donors, 5.3% (n=3711) were repeat donors and only 0.29% (n=203) donors were deferred. Among those who were not deferred, 0.31% (n=214) were excluded due to missing clinical data; making the retention rate for the study to be 99.7% (n=65 535).
Flow chart indicating selection of the blood donors.
Baseline characteristics of the donor study population
All donors’ demographic and donation variables are shown in table 1. Over half of the donations 42.3% (n=27 692) were from the year 2018 and the least number of donations 25.9% (n=16 975) were in 2019. The mean age of the blood donors was 30.6±11.2 years (range: 15–65 years). The vast majority of the blood donors 84.2% (n=55 210) were men with a male to female ratio of 5.5:1. Majority of the blood donors in this study 78.3% (n=51 336) were voluntary donors. In this study, we defined replacement donor as a situation when a friend or family member of the recipient donates blood to replace the stored blood used in transfusion, ensuring a consistent supply.9
Background information of the blood donors in the study (N=65 535)
The frequency and distribution of ABO blood groups have been found to show variation across different regions globally. For almost 3 years the frequency and distribution of the ABO blood groups for three compared regions (Africa, Asia and Europe) the percentage of the A, B, AB and O blood groups still follows the O>A>B>AB trend (table 2).
Publications from various regions of the world indicating frequency and distribution of ABO blood groups
The distribution of donor blood types by their age groups is listed in table 3. The majority 86.7% (n=24 655) of the first-time blood donors were voluntary donors in all age groups. Almost one-third 29.5% (n=5059) of the replacement donors were in the age group of 26–35 years. The oldest age group (56–65 years) accounted for the least number of blood donors 2.8% (n=1840).
Age distribution of the blood donors according to their type (N=65 535)
The frequency and distribution of the ABO and Rh blood groups among donors based on age, sex, type of donor, region of residence and year of donation is shown in table 4. The prevalence of men with blood group O was significantly higher than that of women (60% vs 8.5%) (p=0.002). There were more donors with blood group A from Manyara region than all other regions although the difference did not reach research statistical significance (p=0.621). We also observed that, the prevalence of elderly donors (56–65 years) with Rh negative antigen was significantly higher than that of all other age groups (p=0.013). There were no significant differences for ABO and Rh blood groups (p=0.419).
Frequency and distribution of the ABO and Rh blood groups among donors based on age, sex, type of donor, region of residence and year of donation (N=65 535)
The overall prevalence of Rh negative antigens was 4.7% (n=3074) and 4.6% (n=741), 4.2% (n=524), 4.5% (n=118) and 4.9% (n=1691) for blood group A, B, AB and O, respectively. The variation in the distribution of Rh negative antigens across the blood groups was not statistically significant despite blood group O having a relatively higher prevalence of Rh negative antigens compared with other blood groups (table 5).
Distribution of Rh antigens per ABO blood group among participants (N=65 535)
Discussion
In Tanzania, there is scarce information regarding frequency and distribution of ABO and Rh blood groups among blood donors although of data which have been reported from studies with small sample size.8 10 In this study, we aimed to assess the frequency and distribution or pattern of ABO and Rh blood group systems in a sample population of first-time blood donors. Our study included a larger sample size compared with other previous studies that were done in Tanzania. The majority of blood donors were voluntary donors and blood group O was most prevalent. These key findings may help in explaining the common patterns of blood groups among blood donors in Tanzania.
Majority of blood donors in the present study were men. This is similar to the finding to the studies which have been done in developed and developing countries.8 10–12 Frequent failure of women to meet the required cut-off point of haemoglobin of 12 gm/dL for them to donate blood has been linked to low percentage among female blood donors has been found to be higher in developing countries compared with developed countries.13 A number of contributing factors for them to have low haemoglobin include menstrual cycle, menorrhagia, prenatal iron deficiency anaemia and postnatal blood loss.14 15 Additionally, one study in Europe reported that women are so prone to adverse reactions associated with blood donation particularly vasovagal events which also prevents them from being frequent blood donors.16 Furthermore, traditionally, in most countries in Africa, women are considered generally that are physically unfit for them to donate blood unlike men.17 18 Another study which was done in Brazil reported that religious beliefs has an influence in modifying the attitude of an individual towards blood donation and it was found to have negative impact among women.19
By far, young individuals (aged not more than 35 years) were the majority of blood donors in the present study who consisted of almost 70% of all blood donors in the study. This is consistent with many studies done in Africa.8 20 Being physically fit, mobile and having good awareness, all have been reported to motivate the youths to donate blood. On the other hand, the low rate of blood donation among old individuals has been pointed out that, elders are associated with chronic disease including ischaemic heart disease, diabetes mellitus, malignancy and hypertension.21 However, the age profile for donors in our study is quite different from the one seen in donors from European countries in which there is a significant number of elderly donors compared with the donors in our study and other reported studies in other developing countries. This has once been explained due to increased demand of blood transfusion and low number of blood donors in most European countries which prompted an increase in the age limit for donors as a way of trying to meet the demand for blood.22 Also, the observed difference in the life span between European countries and those in African countries, may explain the difference of the age profile of donors between the two compared regions.
Regarding association of the studied factors with ABO and Rh blood groups in the present study, we observed that, sex was significantly associated with ABO blood groups. This is similar to the observation of the studies which were done in Ghana23 and Iran24 but different from the study of Jahanpour et al in which there was no association between sex patterns of the ABO blood groups.8 This association between sex and ABO blood groups could be by chance and not true association.
Concerning association of ABO blood groups and ethnic groups, a study which was done in Cameroon25 and another one in Ghana26 both reported association between ABO blood groups and ethnic groups. We also observed an increased prevalence of blood group A among donors from Manyara region as compared with other regions (Kilimanjaro, Arusha and Tanga) although the difference did not reach research statistical difference. This may perhaps explain different geographical and population distributions of the antigens determining the ABO blood groups.
In Tanzania and even in the East Africa region, for the past 3 years, blood group O has remained to be the most common ABO blood group followed by blood group A. This is similar even in other regions including Asia and Europe in spite of the slight high proportion of blood group A compared with blood group O that has been reported in some European and Asian countries.27 28 Blood group AB has consistently remained with low proportion for the past 3 years and even beyond that period implying that, across different races and geographical regions globally, blood group AB has significantly low proportion. Some conditions have been reported to be linked with certain blood groups. For example, recently, it has been found that, a significant number of patients with COVID-19 disease caused by SARS-2-COVID have blood group A. This contributes to a shift in frequency of dominancy of blood group O as it was found elsewhere.29 30 Individuals who are Rh negative produce anti-D if they are transfused with blood which is Rh positive.31 The proportion of blood donors in the present study with Rh negative was 4.7% still low when compared with 2% which was reported in Tanzania from a study which had a sample size of 1845 blood donors which is quite insignificant when compared with 65 535 blood donors in the current study. Studies have shown that the incidence of Rh negative may stand up to 17% globally.5 32
The strengths of our study is that it included a large sample size compared with previous studies which were done in Tanzania on frequency and distribution of ABO and Rh blood group systems. Additionally, our study included only first-time donors which is important in assessing willingness of individuals to donate blood. However, we were not able to analyse other blood group systems such as A1, A2, A3, Aw, Ax and Ael due to financial constraints.
In conclusion, our findings have shown that blood group O and AB were the most common and least types of blood groups, respectively. Also, most of the donors were men with ages ranging from young age to middle adult age. Therefore, there is a need for increasing awareness among young individuals in the country, which may help in increasing the amount of blood collected from the blood transfusion centres available in Tanzania.
Data availability statement
Data are available upon reasonable request. Data that were used in this study are available on reasonable request from the manager of the blood bank using email: northernzonebtc@org.tz
Ethics statements
Patient consent for publication
Ethics approval
Ethical approval was obtained from the review by ethical committee of the Kilimanjaro Christian Medical University College (KCMUco) (approval number 2451). Participants gave informed consent to participate in the study before taking part.
Acknowledgments
We thank all workers at the Northern Zone Blood Transfusion Center for being supportive.
References
Footnotes
Contributors EAMV, JY and AM: conceived, designed and wrote the first draft of the study, EM, EDM and EO: data curation, methodology and organisation of the study. All authors revised the manuscript critically and EAMV accepted to be the guarantor of the work.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Disclaimer The views endorsed in this paper are those of the authors and do not necessarily reflect the official policy or position of the Department of Pathology, Kilimanjaro Christian Medical University College in Tanzania.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.