The RISE study was designed, in part, to evaluate the effects of blood donation intensity on iron and hemoglobin status and assess how these are modified as a function of donor demographic, reproductive and behavioral factors, and to provide data to help formulate optimal whole blood donation frequency guidelines. The analysis of the enrollment data from RISE presented here provides the largest and most comprehensive study to date of blood donor iron deficiency.
There have been three previous large cross-sectional studies that evaluated blood donor iron status. Finch, et al,3
used the newly available ferritin assay in 1977 to study blood donors. Ferritin was significantly lower in frequent than in first time donors, and the proportion of donors with ferritin <12 ng/mL increased as the number of donations in the previous year increased. Simon, et al. performed a similar study, but with additional information on female donor menstrual status and on use of over-the-counter iron supplements.1
Ferritin values at any donation frequency were higher in non-menstruating compared with menstruating women; and among menstruating women, in those taking self-administered iron supplements. Most recently Radtke, et al. studied German blood donors in a similar manner,17
but also evaluated sTfR and a number of red cell and reticulocyte indices. Using ferritin < 12 ng/mL as an indicator of reduced iron stores, their findings were similar to those of Finch.
Analysis of the enrollment data from the RISE study shows that absent iron stores – AIS, and iron deficient erythropoies is – IDE, are highly prevalent in frequent blood donors. Of RISE frequent male blood donors 16.4% have AIS and 48.7% IDE, while 27.1% and 66.1% of female frequent donors have AIS and IDE, respectively. In contrast to previous studies, two distinctly different donor groups were included in the RISE study. A first group consisted of first time and reactivated donors. We found no meaningful differences between FT and RA donors when controlling for other factors and the two groups were combined for most analyses. These donors were assumed to have an iron status that was unaffected by blood donation preceding enrollment. In the second group, we enrolled frequent whole blood and red cell donors who had a wide range of donation intensities measured over the previous 2 years. The RISE enrollment results are similar to the previous three studies in that donors’ gender and previous donations were the most important factors in determining iron status. In this study we chose to use a specific measure of iron loss, reflected by ferritin < 12 ng/mL (AIS), and a more sensitive measure of iron loss than previous study,17
log (sTfR/ferritin) >2.07 (IDE). As expected, our more sensitive definition resulted in a higher percentage of blood donors found to have IDE.
Deferral for low hemoglobin is the most common cause of presenting donor loss, particularly in females. Based on data from the REDS-II donor centers, 9.9% of all donation attempts (17.7% females; 1.6% males) end in a deferral for a low hemoglobin or hematocrit.21
Accepted blood donors are required to have a hemoglobin value of at least 12.5 g/dL in the United States.22,23
However, based on currently accepted hemoglobin reference ranges for all adults,24
some female blood donors with values within the reference range are deferred, while some male donors who are below the reference range are eligible to donate. An analysis of NHANES II data for adults shown to have adequate iron stores25
also shows that 12.5 g/dL is not an appropriate lower limit for blood donation to prevent iron depletion.
We confirmed that there are only minimal changes in donor hemoglobin in frequent donors as a function of prior donation intensity, replicating Simon, et al.1
The results, however, are likely directly influenced by the cross-sectional nature of the study designs, since donors who became anemic as a result of iron depletion would have been expected to be deferred from previous blood donation, and hence not included in the group of frequent donors. Given the high rate of hemoglobin deferrals in the 6 REDS-II blood centers,21
this culling effect of deferred donors is likely to be significant. Our study also was limited in that we only enrolled donors who passed the operational requirements at each blood center. Thus, the prevalence and degree of anemia in presenting blood donors was not assessed. For these reasons, this study is unable to provide any information regarding the value of hemoglobin screening to detect iron deficiency or recommend any specific hemoglobin cut-off. Other studies, however, have addressed this issue and concluded that the hemoglobin screen is a poor assessment of the iron status of blood donors.17, 26
We expect to be able to address these hemoglobin cut-off issues in our follow-up study of these cohorts in RISE.
In our multivariable models for AIS and IDE, previous donation intensity was by far the most important predictor of iron deficiency and iron deficient erythropoies is at enrollment. The magnitude of the associations between AIS or IDE and a variety of donor characteristics is a new and significant additional contribution of RISE. The following donor characteristics, in addition to donation intensity and gender, were found to be independent predictors of AIS and/or IDE: age, weight, smoking, use of iron supplements, HFE genotype, and menstrual and pregnancy status. Country of birth and one dietary variable, consumption of other fish, were marginally significant for IDE.
The inclusion of age, along with a separate assessments of menstrual and pregnancy status in the model, tended to blunt the observed gender effect in this analysis. The observed odds ratio for female gender, reflects a residual gender effect after adjustment for age and menstrual and pregnancy status, and probably reflects the residual iron depletion found in older, non-menstruating women compared to men. The independent influence of menses and pregnancy presumably reflects their known synergistic effect of lowering iron stores. Asian donors had a lower prevalence of IDE and were less likely to have IDE than whites in the unadjusted model. This association was not seen in the multivariable model and it is not clear if the latter finding relates to the country of birth differences or if the unadjusted ethnicity relationship might be due to genetic differences or to environment factors, for instance diet. One large report describes higher ferritin levels in Asians than in Caucasians, which is unrelated to HFE genotype.5
Presumably, this could explain the differences we observed.
The influence of weight on the development of AIS/IDE is not surprising, since a blood donation represents an increasing percentage of red cell mass in smaller donors and since approximately 85% of body iron is found in the erythron. The independent effect of a tendency to lower weight in female donors tends to aggravate the existing female disadvantage in iron homeostasis.
Smoking had an apparent protective effect of blood donors’ iron status. This was somewhat unexpected since smoking is known to increase hemoglobin levels.27
It was expected that the higher hemoglobin level might allow smokers to donate more frequently at lower iron levels. However, one cross-sectional study in 788 women of menstrual age found that smoking lowers the sTfR, but not the ferritin after adjusting for all other measured variables.28
This finding, if confirmed, could relate to our observation of higher odds of IDE, but not AIS in non-smokers. It is not clear from the cited study if this finding is a laboratory artifact with the sTfR assay or if it represents real differences in iron homeostasis.
Iron supplements were reported to be taken by 39% of RISE donors. Since the actual multivitamin or mineral supplements were not audited to determine their iron content, this result needs to be interpreted with some caution. However, such donors had a significantly lower prevalence of AIS in the adjusted model suggesting that low dose iron supplements may be beneficial in ameliorating iron depletion. However, the actual magnitude of the effect was small (15.2% AIS in non-supplement donors vs. 14.9% AIS in supplemented donors).
HFE genotype was independently associated with IDE in the adjusted model. However, the effect appears to be due to homozygote or mixed heterozygote genotype for C282Y and H63D. A transferrin polymorphism, G277S, which has been associated with an increased prevalence of iron deficiency anemia in menstruating women,4
was not associated with AIS or IDE. A more detailed genetic analysis of the RISE donors is planned.
A variety of dietary variables were included in the model. The foods chosen for inquiry were primarily iron-rich foods. However, the only food that was significant in the multivariable model was other fish (defined as consumption of fish other than iron-rich clams, oysters, mussels, shrimp and sardines). Surprisingly beef and liver consumption, which are often recommended to blood donors, had little to no effect after adjusting for other factors. It would appear based on the self-reported RISE dietary variables, that consumption of these foods does not have a meaningful impact on blood donor iron status. More comprehensive dietary surveys would have been desirable, but RISE data was limited by the desire to restrict the length and complexity of the questionnaire. Therefore the lack of dietary effects may be due to the inaccuracy of our measures of iron-rich food consumption, especially given that donors were asked to generalize about their dietary habits over a long period of time. It is also possible that diet would be more important in other countries. Nevertheless, diet does not seem to be a particularly fruitful area for this investigation given the data from our dietary questionnaire, but analysis of the longitudinal data will be important to verify this.
The six REDS-II centers each enrolled an approximately equal number of donors. When blood center was included in the multivariable model, center E was associated with higher levels of AIS and IDE, even after adjustment for multiple donor characteristics that may differ between centers. Since center A was the only center using 450 mL whole blood collection containers, we also analyzed the results from center A versus the other 5 centers combined. However, no significant difference in the odds of AIS or IDE was found in center A donors compared to donors at the other 5 centers, and the remaining 5 centers continued to show difference among them in the odds of AIS and IDE, after center A was removed. The explanation for this overall finding is not certain. It is possible that unrecognized methodological differences existed between center E and the others or that the statistical model did not adequately control for underlying donor differences between centers. The finding of differences among centers illustrates the shortcomings of single center studies since a study done at center E might come to different conclusions than at the other centers. As the REDS-II centers are geographically diverse and chosen to represent the U.S. blood supply, RISE as a multi-center study is likely to better reflect the characteristics of U.S. blood donors as a whole than single center studies.
A limitation for the current analysis is the cross-sectional nature of the enrollment data. This raises the possibility that previously deferred donors may no longer be donating; hence, the magnitude of iron depletion and or anemia may be underestimated. Other possible limitations include errors inherent in self-reported weight and diet. Finally, the use of peripheral blood assays, rather than bone marrow examinations, to assess donor iron status leaves open the possibility of interpretation error based on inferences about donor iron status (AIS and IDE). However, the RISE study is a large, geographically diverse evaluation of blood donor iron status which includes a comprehensive evaluation of donor demographic, genetic, and behavioral factors and their relationship to iron deficiency. As such it is a unique resource for understanding factors that impact on donor iron stores.
In summary, the enrollment data from RISE confirm previous studies documenting a high prevalence of AIS and IDE in frequent blood donors and confirm the strong association between prior donation intensity and the presence of AIS/IDE. In addition to the well known relationship between iron depletion and female gender as a result of menstruation and pregnancy, AIS and IDE in donors are also significantly associated with donor weight, presumably as an indicator of red cell mass. These three factors together are readily apparent in the individuals presenting at blood drives and could be readily manipulated to reduce the prevalence of AIS or IDE by altering standards for frequency of whole blood and double red cell collection to relate allowable donation frequency to donor gender and size. Iron supplementation of blood donors has been proposed for routine implementation and several pilot operational and clinical trials have been conducted.9
However, operational as well as medical/legal/ethical obstacles have prevented widespread implementation of iron supplementation to date. Based on this study, the impact of low dose iron supplementation could be relatively modest, in part because many blood donors appear to already been taking supplements; on the other hand, it is possible that an increased dose, or programs that ensure donor compliance may still be beneficial. A comprehensive multi-center clinical trial of iron supplementation is warranted. This study suggests that other potential interventions, such as changing the consumption of iron-rich foods or alteration of smoking habits, would likely not be effective. Finally selecting donors on the basis of inherent factors such as race/ethnicity, country of birth and genetic makeup (as far as can be measured) would appear to have limited influence on AIS/IDE.
Given the widespread and frequent occurrence of blood donation, optimizing its safety for volunteer donors requires significant attention. It appears likely that the findings reported here will stimulate analysis of the health importance of iron depletion in blood donors and the ability of the current donor standards to prevent and detect significant adverse donor sequelae related to iron depletion. They should also cause consideration of interventions to better manage donor iron balance. Reducing the frequency of blood donation would reduce the prevalence of iron deficiency among blood donors, as might implementing routine iron supplementation. In addition to the data presented here, decisions on these interventions will depend on the prospective data obtained after follow-up of the RISE cohort is completed as well as the assessment of the health significance of iron deficiency.