Prof. Dr. Andreas Greinacher, Institut für Immunologie und Transfusionsmedizin, Ernst-Moritz-Arndt-Universität Greifswald, Sauerbruchstraße, D-17489 Greifswald, Germany E-mail: firstname.lastname@example.org
The population structure in most European countries is currently changing with a shift from younger to older age groups. Only sparse data exist on the impact of these demographic changes on future blood demand and supply. Data on blood recipients are sparse and unconnected to data on blood donors. Based on studies in North America and Europe on the impact of demographic changes on future blood supply, the demographic trends will affect many regions in the Western world similarly. These effects are most pronounced in the new member states of the European Union where birth rates declined abruptly after 1989. Co-ordinated efforts will be required to prevent blood shortages based upon these demographic trends in Western societies. The second part of this review provides examples of different methodological approaches to obtain data on the sociodemographic background of the blood donor population.
Blood supply can be defined as a transfer of blood from the population of donors to the population of recipients. These two groups differ considerably in their demographic structure. The donor population consists primarily of young, healthy individuals, while most patients requiring blood transfusion belong to the age groups above 60 years. These major differences of age distribution between the two groups render demographic trends important for future blood supply. The demographic change causes a double effect, reduction of the eligible donor population with a concomitant increase of patients requiring blood transfusions .
Because of an increase in life expectancy, ageing of previous high birth rate cohorts, and a more recent decrease in birth rates with stabilization at a current low level, the population structure in most countries of the Western world is currently shifting from younger to older age groups. Despite a decline in total population, the absolute numbers of older patients will increase resulting in a disproportionate increase in patients with malignancies and other diseases requiring major surgery . Treatment of these patients will require sufficient blood supply.*
Studies on the impact of demographic changes on the blood supply
In 1994, Vamvakas and Taswell estimated for the US the demand of RBC transfusions to increase by 64% from 1989 till 2030, particularly because of a population growth among the population over 65 years of age. The number of blood units collected was predicted to increase by only 12% over the same time period, suggesting a potential shortfall of RBCs [3,4].
Zou et al.  analysed the data base of the American Red Cross Blood Service for changes in age distribution among blood donors between 1996 and 2005. They found donations by repeat donors of 50 years or older increased from 22·1% in 1996 to 34·5% in 2005, whereas the < 50 years age groups that used to account for the majority of the repeat donors are shrinking in their share of the total donations from 59% in 1996 to 48% in 2005. Adjusted for general population trends, the effective number of donors decreased by more than 10% in repeat donors in the age group 20–49 years; and repeat donors in the age group 25–39 years even decreased by > 40%. An alarming signal of this study is that despite an increased number of first-time donors between 16 and 19 years had been recruited, this did not translate in an increased number of repeat donors for the same or older age groups as these donors were poorly retained. The authors predict a severe shortage of blood components in the foreseeable future unless the present trends are offset by significantly increased supply or reduced usage of blood and blood components.
Data on European blood donor populations are sparse. It remains unclear whether this is related to a lack of studies, or whether also language issues are an important factor. Interestingly, one of the most comprehensive nation-wide studies on the blood donor population has been performed in Germany by the Robert Koch-Institute (; see below) but this study is reported in German language and is therefore not generally available.
In 2004, Currie et al.  calculated the future increase in blood demand based on the analysis of in-hospital patients of two major hospitals of the year 1999. Patients aged > 70 used 46% of the blood supply, whereas patients aged < 30 used 10%. They predicted a 29% rise in blood demand until 2026 compared to 1999 primarily because of the increase in age groups with the highest rates of transfusion. Because of a considerably large proportion of children and young adults in the UK population, these authors projected almost no decrease in blood donations and concluded that the future supply/demand ratio (1:1·29) is likely to remain rather stable.
The eastern part of Germany faces more pronounced demographic changes compared to other Western European regions. Reasons for the rapidly shifting demographics include: a sharp decline in birth-rate by about 50% between 1989 and 2004; negative migration patterns (young people – primarily women – have left for Western Germany), and a sharp increase in life expectancy following reunification of Germany (mean of 5·1 and 4·8 years for men and women, respectively, since 1989) [8,9].
Using the data of the blood donors at the Greifswald Department of Transfusion Medicine and the data of the patients of the main catchment area of the University Hospital of Greifswald, we projected blood donation rates and blood demand rates to the year 2015 .
A major and unexpected finding of the study was that the expected decrease in blood donations that results from a relative decrease in the younger donor population will have a higher impact on the blood supply than the increase of blood demand by an increase in the older age groups (Fig. 1). The most pronounced decrease will occur in the age group 20–24 years, with a projected decrease of 60% by 2015. This will be the major determinant for the decrease in blood donation (−30% by 2015). At the same time, the proportion of people 70 years of age and older will increase from 11% to 19%. Based solely on the projected demographic changes and all other determinants assumed constant, the demand for RBCs will therefore increase by +12% units in 2015 compared to 2004.
The same trend as in Greifswald has been found in Magdeburg, the capital of the Federal State of Saxonia-Anhalt. In this city, the population percentage of the age group 18–68 years, which is the age group of potential blood donors will decrease from 72% to 65% within 10 years .
Next, we extended our study to an entire federal state in Germany, Mecklenburg-West-Pomerania, by analysing all in-hospital blood recipients and all blood donors in this state for the year 2005. Preliminary data of this analysis showed that about 120 000 RBCs were donated in a total population of 1·2 Mio in the age groups eligible for blood donation (18–68 years). The distribution of the donor population had two peaks at 20–24 years and at 40–44 years, respectively. With the decline in population of younger age groups, this will cause a decline in the overall blood donation rate of at least 20%. Interestingly, the different blood donor services in the state complement each other by recruiting different age groups for blood donation. Blood donors donating at the Red Cross blood donation service had a median age of about 42 years, while the blood donors donating at the hospital-based donation services had a median age of 28 . Thus, a diversified blood donation system with several institutions seems to have the advantage of different strategies of donor recruitment which attract different age groups of the general population.
Also in this study the majority of RBCs (62%) were transfused to patients ≥ 65 years. When we used these data to project the shortfall of RBCs, we again found that the increased demand for blood coincides with a significant reduction in blood donations, resulting in an overall shortfall of RBCs of > 30% until the year 2020 .
The Robert Koch-Institute provided a comprehensive analysis of the demography of blood donors in Germany based on the 2006 data on blood donors annually reported by all blood donation services in Germany. In 2006, the German population in the age groups eligible for blood donation according to national regulations, i.e. 18–68 years, was 56·3 Mio. Overall, about 4% of this population donated blood in 2006 with 4 702 384 whole blood donations. Of those the vast majority, 4 284 413 units (91·1%), were donated by 2 224 382 repeat-time donors.
First-time donors and repeat-time donors differed in their structure. First-time donors primarily belong to the younger age groups. More than half of the first-time donors were in the age group 18–24 years, while only 3·3% of first-time donors were older than 55 years. Of the repeat-time donors, most (50·9%) were in the age groups 35–54 years; 18% were 55 years of age or older and will therefore likely leave the pool of blood donors within the next 10 years. With the exception of the 55 year and older age group, the age group distribution of blood donors was similar to the age group distribution of the general population.
Women are more motivated to donate blood compared to men as shown by the fact, that 61·1% of those willing to donate for the first time were women. However, the gender distribution of those who actually donated blood as first-time donors was very similar between women and men (50·8% vs. 49·2%). In repeat-time donors, the percentage of men was even higher (54·1%). This likely reflects the higher deferral rate of women, most likely because of a higher prevalence of iron deficiency in women. In the context of the demographic change, these data clearly indicate that the over-proportional increase in the older age groups, which will occur over the next two decades, will cause a shortfall in blood supply if age-specific blood donation and blood transfusion rates remain stable. Especially younger blood donors in the age group of 25–34 years need to be motivated to donate blood more frequently.
Blood donor research: potential use and possible methods
The following section does address how a representative analysis of the blood donor population with regard to their social background and motivation could be designed and analysed (summary of a more extensive publication on this topic recently published elsewhere ).
The regional context of such analyses is of major importance as it is very unlikely that the same criteria and strategies apply for those living in major urban areas as well as for those living in smaller cities or in villages. Designing interventions to increase the number of blood donors requires information about the characteristics of those who donate blood but also about those who do not. The most accurate approach would be a population representative survey in the target region. However, as the proportion of blood donors in the population is low (usually < 5%), the sample investigated in such a survey must be very large to achieve sufficient statistical power, making such a study too costly. Alternative approaches are either questioning blood donors in the context of the blood-donating procedure only or including additionally data from a general population representative survey performed in the region where the respective blood donating centre is located.
Applying data only from blood donors
A survey performed with the blood donors in the course of the blood-donating process should fulfill three conditions:
1 The survey should last 1 year. This is important because there might be seasonal variations in the behaviour of the blood donors as well as in the activities of the blood donation centre. With a survey interval of 1 year, most of these variations will level out.
2 People enrolling for donating blood should be approached for study participation in constant intervals over the whole time the donation centre is open. This is important because different groups of people might prefer different times for donating blood, e.g. those donating during morning hours might represent a different subgroup of the population than those donating after regular working hours. It is therefore important that everybody has the same chance to participate in the study.
3 For each participant, the number of blood donations given within the study year must be recorded. This is important because this is one central information for determining those features that are associated with the tendency of donating blood.
Veldhuizen et al. in 2009  used this approach to study the contribution of demographic factors to the donor career to gain insight into the demographic profile of active vs. resigned donors, and frequent vs. occasional donors. For this they analysed all registered Dutch whole-blood donors for a 1 -year period (2004; n = 370 470). They found the proportion of donors adhering to donation was smaller among women when compared to men [odds ratio (OR) 0·73, 95% confidence interval (CI) 0·72–0·75]. Other factors reducing the risk to resign from blood donation were an age above 24 years, a high income, living in less urbanized areas or areas with relatively few ethnically diverse people. The authors also found that men were five times more often frequent donors than women (OR 5·27, 95% CI 5·15–5·39) and that these frequent donors are more likely to live in urbanized areas and have a higher income than occasional donors.
The interdisciplinary approach including geographical and population census data
The transfusion medicine research group at McMaster University, Hamilton Canada, together with the Department of Geography and Earth Sciences used a geographic approach to correlate sociodemographic information and the frequency of blood donation . They used geo-coded blood donor and donor clinic data. Geo-coded data are data on the sociodemographic structure in a defined geographic area. This type of information is frequently used by companies for designing advertisement campaigns or for the decision process to allocate a new facility or store. Based on the postal zip codes, blood donors were allocated to certain areas. For the years 2006–2007, this information was matched with social and economic characteristics, as well as descriptors of city size and geographical location and accessibility of the donation clinic. Canada is performing a regular population census in which detailed information of social and economic characteristics of small regionally defined areas is collected. The authors identified several factors associated with a higher number of blood donations in urban areas such as: areas with a higher proportion of younger residents, good English language skills, a low proportion of people with immigrant status, higher education levels in the area, and easy accessibility of the donation clinic. This study shows how the combination of existing data and the involvement of knowledge from non-medical areas can be used for blood donor research.
Taking advantage of a population representative survey in the same region
This approach of comparing data of a blood donor survey with those of the general population is feasible in regions where a population representative survey has been performed. In most cases, age and residence will be differently distributed between the individuals enrolled in both surveys. Therefore, these differences should be controlled for by appropriate statistical tests (hypothesis-driven multivariate regression analyses with donation as the dependent, the characteristic in question as the independent and gender, age and residence as control variables).
Recently, the Bavarian Red Cross Blood Donation Service obtained sociodemographic data and information on selected health characteristics and comorbidities from 6016 blood donors . They found more men than women being blood donors but otherwise the donor population age distribution reflected the age structure of the general Bavarian population. However, blood donors more often lived in communities with < 20 000 inhabitants (OR 4·73; 95% CI 3·69–6·13) and were more often born in Germany (OR 2·71, 95% CI 2·12–3·50), and seem to have a lower level of education compared to non-blood donors. A subset of 1187 of these blood donors was further analysed and the data were compared with the data of a long-term cross sectional population health study including the population of the city of Augsburg and two adjacent counties (KORA study). Regular blood donors were generally healthier than the general population. Especially the incidence of myocardial infarction was highly significantly reduced in blood donors compared to non-blood donors (OR 0·17; 95% CI 0·08–0·34). Whether this reduced rate of myocardial infarction is a direct effect of blood donation or whether it is an indirect effect of a general better health and/or more healthier lifestyle in people who donate blood is still unresolved.
The demographic change will cause an increased future demand for blood that coincides with reduction in blood donations. This will inevitably cause shortfalls in blood supply if the percentage of blood donors in all age groups will not be increased. The demographic changes are particularly pronounced in the new member states of the EU (Fig. 2) [16,17]. Only France, the Scandinavian countries and the United Kingdom face a somewhat less-pronounced decline in the younger age groups.
Increase in blood donation rates needs systematic blood donor research and targeted, evidence-based intervention ideally by a joint approach of experts in epidemiology, social sciences and experts in transfusion medicine. The second major approach to counteract shortfalls in blood supply, which has not been addressed in this review, is to optimize medical practice to decrease unnecessary blood transfusion whenever possible.
This review is a summary of the presentation given by one of the authors (AG) at the ISBT meeting June 2010 in Berlin, Germany. There is considerable overlap with other publications of the same authors.