Sociodemographic and Clinical Determinants of Repeated Blood Donation in Luanda, Angola

1. Introduction

Blood availability is a cornerstone of healthcare systems and is particularly critical in sub-Saharan Africa, where transfusion demand is high because of the substantial burden of maternal and childhood anaemia, trauma, and surgical complications [1,2].

The World Health Organization (WHO) recommends that 1–3% of the population donate blood annually, with emphasis on voluntary non-remunerated blood donors [3,4]. Repeat blood donation is widely recognized as a key determinant of a safe and sustainable blood supply [4]. Compared with first-time donors, repeat donors generally present a lower prevalence of transfusion-transmissible infections, regardless of donor type, because repeated donation progressively selects individuals with lower-risk behaviours [5,6]. In Europe, approximately 90% of blood donations are collected from regular donors, whereas in sub-Saharan Africa this proportion is only about 38% [3].

Previous studies conducted in Africa have identified several determinants of donor retention, including gender, age, educational level, donor type, altruistic motivation, social norms, knowledge about blood donation, and barriers such as fear of needles and cultural beliefs [7,8,9,10,11,12]. Nevertheless, repeat blood donation may also increase the risk of iron depletion and iron deficiency anaemia, as routine haemoglobin screening is unable to detect early depletion of iron stores [13,14,15]. In Angola, evidence on the determinants of repeat blood donation remains scarce [16]. Therefore, this study aimed to identify the sociodemographic and clinical determinants of repeated blood donation among blood donors in Luanda, the capital city of Angola.

2. Materials and Methods

2.1. Study Design and Setting

This cross-sectional study was conducted among blood donation candidates attending the Angolan National Blood Institute, located in Luanda, Angola, between June 2025 and February 2026. A total of 189 blood donation candidates were consecutively recruited during the study period. The study was conducted in accordance with the principles of the Declaration of Helsinki and approved by the General, Technical and Scientific Management of the National Blood Institute of Angola (approval number 201/GDG/INS/2026). Before enrolment, all participants received detailed information about the study objectives and procedures and provided informed consent. Confidentiality and anonymity of all collected data were guaranteed throughout the study.

2.2. Data Collection and Laboratory Procedures

Data were collected using a questionnaire administered by trained healthcare personnel. Sociodemographic information included age, gender, educational level, area of residence, employment status, donor type (replacement or voluntary), and history of previous blood donations. Approximately 5 mL of venous blood was collected from each participant into EDTA tubes following standard blood donation procedures. Haemoglobin concentration was measured using the Mindray BC-780 Auto Haematology Analyser (Mindray, Germany), according to the manufacturer's instructions. Anaemia was defined as a haemoglobin concentration <12.0 g/dL, and participants were classified as anaemic or non-anaemic. Age was analysed both as a continuous variable and categorised into <30 years and ≥30 years. Educational level was classified as illiterate, basic, secondary, or higher education, while area of residence was categorised as Luanda capital or other municipalities. Employment status was classified as employed or unemployed, and donor type as replacement or voluntary. The outcome variable was donation history, categorised as ≤2 previous blood donations and >2 previous blood donations.

2.3. Statistical Analysis

Statistical analyses were performed using RStudio v2026.04. Continuous variables are presented as median and interquartile range (IQR), whereas categorical variables are expressed as frequencies and percentages. Comparisons between donors with ≤2 and >2 previous blood donations were performed using the Mann–Whitney U test for continuous variables and the Chi-square test or Fisher's exact test for categorical variables, as appropriate. Univariate logistic regression analysis was performed to assess the association between sociodemographic and clinical characteristics and repeated blood donation (>2 previous donations). Variables considered clinically relevant or showing evidence of association in the univariate analysis were entered into a multivariate logistic regression model to identify factors independently associated with repeated blood donation. Odds ratios (ORs) and adjusted odds ratios (AORs) with their corresponding 95% confidence intervals (CIs) were calculated. All statistical tests were two-sided, and a p<0.05 was considered statistically significant.

3. Results

Table 1 presents the demographic and clinical characteristics associated with repeated blood donation (>2 previous donations) among blood donors. A total of 189 donors were included in the analysis, of whom 14 (7.4%) had donated blood more than twice, while 175 (92.6%) had donated two times or fewer. The median age of the study population was 31 years (IQR: 25.0–38.0), with no statistically significant difference between donors with ≤2 and >2 previous donations (31.0 vs. 34.5 years, p=0.360). Similarly, the distribution of age groups did not differ significantly (p=0.173), although donors aged ≥30 years were more likely to have donated more than twice than younger donors [OR: 2.26, (95% CI: 0.68–7.46), p=0.183]. This association remained non-significant after adjustment for potential confounding factors [AOR: 2.83, (95% CI: 0.74–10.78), p=0.127]. The proportion of male donors was higher among repeat donors (78.6%) than among donors with ≤2 donations (61.1%). Although the association was not statistically significant, male donors had higher odds of repeated blood donation [OR: 2.33, (95% CI: 0.63–8.65), p=0.206]. After adjustment, male gender emerged as an independent factor associated with repeated blood donation, with males being nearly six times more likely to have donated more than twice than females [AOR: 5.81, (95% CI: 1.14–29.6), p=0.034]. Educational level was not significantly associated with repeated blood donation (p=0.153), and odds ratios could not be estimated for the illiterate category because no repeat donors were observed in this group. Also, area of residence was not associated with repeated blood donation (p=0.757). Donors residing outside Luanda capital showed similar odds of repeated donation compared with those living in the capital [OR: 1.19, (95% CI: 0.40–3.53), p=0.757], and this finding remained unchanged after adjustment [AOR: 1.22, (95% CI: 0.36–4.10), p=0.753]. Employment status was also not associated with repeated blood donation (p=0.158). Although employed donors were more likely to have donated more than twice than unemployed donors [OR: 2.50, (95% CI: 0.67–9.29), p=0.170], this association was not maintained in the multivariable model [AOR: 2.05, (95% CI: 0.50–8.47), p=0.319]. Regarding donor type, voluntary donors were more frequently represented among repeat donors (28.6%) than among donors with ≤2 donations (11.4%). Although voluntary donation showed a trend towards an increased likelihood of repeated donation [OR: 3.10, (95% CI: 0.89–10.82), p=0.076], the association was no longer evident after adjustment [AOR: 2.08, (95% CI: 0.48–9.01), p=0.326]. Regarding clinical profile, median haemoglobin concentration did not differ significantly between donors with ≤2 and >2 donations (11.5 vs. 11.43 g/dL, p=0.763). Interestingly, anaemic donors had higher odds of repeated donation than non-anaemic donors [OR: 1.91, (95% CI: 0.51–7.12), p=0.333], but this relationship remained statistically non-significant after adjustment [AOR: 3.36, (95% CI: 0.77–14.58), p=0.106].

4. Discussion

To the best of our knowledge, this is the first study to describe determinants of repeat blood donation in Luanda, Angola. In the present study, male gender emerged as a factor independently associated with repeat donation (>2 previous donations), conferring nearly sixfold increased odds (AOR: 5.81, p=0.034). Additionally, we observed non-significant trends suggesting higher odds of repeat donation among individuals aged ≥30 years, voluntary donors, and donors with anaemia. These findings provide insights into donor retention patterns in Luanda and highlight structural and biological challenges that may affect the sustainability of the blood supply system in Angola.

The strong association between male gender and repeat donation observed in our cohort is consistent with reports from multiple African countries, where men represent between 68% and 88% of blood donors [13,17]. In Nigeria, women accounted for only 12% of donors in certain regions, a disparity attributed to sociocultural norms, religious constraints, and physiological factors such as menstruation, pregnancy, and higher baseline prevalence of anemia [18]. Similar findings have been documented in Ghana and Ethiopia, reinforcing the persistent gender gap in blood donation across Sub-Saharan Africa [13,19]. In many African contexts, women face higher rates of iron deficiency and are more frequently deferred due to low haemoglobin levels, which might discourage continued participation and reduce transition to repeat donation [18,20]. In Angola, where anaemia prevalence among women of reproductive age remains elevated, this biological vulnerability likely contributes to lower female retention rates. These findings highlight the need for targeted strategies to increase female participation, including nutritional support, iron supplementation programs, extended inter-donation intervals, and culturally sensitive community education campaigns aimed at addressing misconceptions and sociocultural barriers.

Although not statistically significant, the observed trend toward higher repeat donation among individuals aged ≥30 years suggests that maturity and life experience could influence sustained donation behaviour. African studies indicate that first-time donors are often recruited through school or university campaigns and tend to be younger, whereas older donors are more likely to return for subsequent donations [5,6]. Allain (2011) reported that the donation experience is the most critical determinant of blood safety, since frequent donors consistently have lower rates of transfusion-transmissible infections [6]. The median age of 31 years old in our cohort aligns with findings from Ghana and Nigeria, where median donor ages range from 28 to 30 years [13,15]. Retaining younger donors as they transition into adulthood is therefore essential for long-term blood supply sustainability. Therefore, Angolan public health managers and hospital administrators should consider implementing reminder systems, message reminder programs and donor recognition initiatives have proven effective in improving retention in other African contexts [21,22].

The non-significant association between voluntary donor status and repeat donation in our study contrasts with the WHO's emphasis on unpaid voluntary donors as the foundation of safe blood systems [4]. Indeed, previous studies have shown that first-time voluntary donors are no safer than first-time replacement donors, and that repeat donation is the main determinant of blood safety [5,6]. Replacement donors who subsequently return voluntarily often demonstrate safety profiles comparable to regular voluntary donors [5,6]. This shows that replacement donors who subsequently return voluntarily generally demonstrate safety profiles comparable to those of regular voluntary donors. It is worth mentioning that in contexts where blood shortages are frequent and only a minority of donations come from regular donors, excluding first-time donors can further compromise the supply [3]. In Angola, where blood donation rates are still below WHO targets, public health actions can include awareness campaigns on radio and in communities, support from community and religious leaders to encourage voluntary donation, and mobile blood donation units that reach both cities and rural areas. SMS messages can remind past donors to donate again when they are able. A national donor list can help track and contact donors, and simple recognition like certificates or public thanks can encourage people to return. Teaching about blood donation in schools can also help create regular and voluntary donors over time. In addition, offering flexible donation schedules, ensuring a positive and safe donation experience, and providing basic donor feedback (such as haemoglobin results or health checks) can increase trust and motivation, making it more likely that donors return and donate regularly.

One of the most interesting findings of our study was the higher odds of repeat donation observed among donors with anaemia, although this association did not reach statistical significance. This apparent contradiction has also been described in Ghana and Nigeria, where repeat donors exhibited higher anaemia prevalence and lower ferritin levels compared to first-time donors [3,13,15]. The phenomenon might be explained by cumulative iron depletion resulting from repeated blood donations, particularly in contexts where screening is primarily based on measuring haemoglobin, which does not detect iron deficiency in its early stages [3]. Serum ferritin, the most sensitive indicator of iron stores, progressively declines with repeated donations while haemoglobin levels may remain within acceptable limits until iron deficiency becomes advanced. Consequently, donors may continue to donate until overt anaemia develops, compromising both donor health and potentially the quality of collected blood [3,23]. In Angola, where iron deficiency is prevalent due to dietary limitations and parasitic infections, the risk of cumulative iron depletion among repeat donors is particularly concerning [24]. These findings highlight the need to consider ferritin monitoring for frequent donors and to integrate iron supplementation and nutritional counselling into donor management protocols to ensure long-term donor safety and retention.

Our study has some limitations. The cross-sectional design prevents causal inference regarding determinants of repeat donation. The relatively small sample size, particularly the low number of donors with more than two previous donations, limited statistical power. The absence of serum ferritin measurements restricted direct assessment of iron depletion, limiting interpretation of the anaemia contradiction observed. Furthermore, the study was conducted in a single urban center in Luanda, which may limit generalisability to rural regions or other provinces of Angola. Despite these limitations, this study provides evidence on factors associated with repeat blood donation in Angola. Our findings emphasise the central role of male donors in sustaining the blood supply, highlight potential gender and biological vulnerabilities affecting donor retention, and increase important concerns regarding iron depletion among frequent donors. Therefore, strengthening retention strategies, improving donor follow-up systems, and integrating iron monitoring into donor care protocols might contribute substantially to building a safer and more sustainable blood supply system in Angola. Further prospective and multicentre studies with larger sample sizes are needed to explore behavioural, clinical, and health system determinants of repeat blood donation in Angola.

5. Conclusion

In conclusion, male gender was independent determinant of repeated blood donation. Non-significant trends suggested higher repeat donation among donors aged ≥30 years, voluntary donors, and employed individuals. The higher frequency of anaemia among repeat donors raises concern about possible iron depletion in a context with limited ferritin monitoring. These findings highlight the need to improve donor follow-up, strengthen female participation, and consider iron status monitoring. Further studies including iron biomarkers are needed to clarify determinants of repeat donation and support safer donor policies in Angola.