Abstract
Cohorts that are non-representative of their target population pose a critical challenge, limiting generalizability and potentially yielding misleading effect estimates. To this end, we conducted a cross-sectional assessment of the representativeness of the Danish Blood Donor Study (DBDS)—a nationwide cohort of 170,000 individuals recruited during visits to blood donation centers across Denmark—relative to the Danish general population aged 18–74 years. Using national register data, we compared demographic, socioeconomic, and health-related characteristics of DBDS participants to those of non-DBDS individuals as of December 31, 2021. Our findings revealed that DBDS participants were more likely to be well-educated, live with an adult of the opposite sex, and have two children. Although individuals living alone were generally underrepresented, young males (18–24 years) and females (18–44 years) in this group were notably overrepresented. In addition, those with high incomes or with employment in finance or insurance were strongly overrepresented, whereas immigrants and rural residents were underrepresented. Participants were less likely to have any recently recorded diagnoses or redeemed prescriptions across most major disease and treatment categories. In particular, individuals with mental, behavioral, or hematological disorders were markedly underrepresented, whereas females (25–44 years) with diagnoses related to pregnancy, childbirth, or the perinatal period—or with redeemed prescriptions for urogenital or hormonal medications—were overrepresented. This characterization of DBDS participants provides context for interpreting results obtained from the cohort and underscores the need for methodological approaches to improve the generalizability of findings derived from non-representative samples.
Data availability
Person-level data from DBDS needed to reproduce this study cannot be made publicly available due to confidentiality legislation. Furthermore, this study is based on pseudonymized register data located on a secure platform at Statistics Denmark. Meta-data and programs are available from the authors upon reasonable request and with permission of the DBDS steering committee, the Ethical Committee, and the Danish Data Protection Agency. Enquiries about legal possibilities for accessing these data within DBDS, scripts/codes and further information should be addressed to the corresponding author.
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Acknowledgements
We thank the Danish blood donors for their valuable participation in the Danish Blood Donor Study, and the staff at the blood centers for making this study possible.
Funding
This study was supported by a grant from the Independent Research Fund Denmark. The Danish Blood Donor Study (DBDS) is funded by an annual grant from Bio- and Genome Bank Denmark. The initiation of DBDS was supported by the Danish Administrative Regions (02/2611) and the Danish Council for Independent Research (09–069412). Additionally, DBDS is funded by the Novo Nordisk Foundation (NNF23OC0082015, NNF17OC0027864, and NNF17OC0027594).
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J.T., M.D., K.M.D., and S.R.O. drafted the manuscript; J.T. performed the statistical analyses; J.T., D.H., M.D., K.M.D., and S.R.O interpreted the data. C.E., O.B.V.P., E.S., and S.R.O. are leaders of DBDS. J.T., D.H., L.A.N.C., L.J.E.Q., C.M., N.B., J.D., K.A.K., S.M., T.H., B.M., M.T.B., B.A., T.F.H., K.R., H.H., A.J.S., T.W., C.E., O.B.V.P., E.S., M.D., K.M.D., and S.R.O. contributed to data curation and infrastructure management. All authors were involved in critically revising the manuscript and approved the final version before submission.
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DBDS was approved by the Central Denmark (1–10–72–95 − 13) and Zealand (SJ-740) Regional Committees on Health Research Ethics and the Data Protection Agency (P-2019–99). All methods were carried out in accordance with the relevant guidelines and regulations (including the Declaration of Helsinki).
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Oral and written informed consent was obtained from all DBDS participants.
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Træholt, J., Helenius, D., Christoffersen, L.A.N. et al. Representativeness of the Danish Blood Donor Study relative to the general population: a cross-sectional assessment. Sci Rep (2026). https://doi.org/10.1038/s41598-026-41941-1
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DOI: https://doi.org/10.1038/s41598-026-41941-1
