BACKGROUND AND OBJECTIVES Efficient blood supply chain requires accurate demand estimates. Blood demand is created by clinicians making transfusion decisions based on patient status. To better understand the use of blood units, we tracked their use hourly and across a large hospital organization. MATERIALS AND METHODS We analyzed blood use in adult patients over 2021-2022 at HUS Helsinki University Hospital, serving a population of 1.7 million and consuming a third of blood units used in Finland. We utilized electronic health records (EHR) to map transfusions to patient demographics, diagnoses, medical specialties, treatment events, surgical procedures, and laboratory values. Data were matched to transfusion of red blood cells, platelets and plasma using timestamps and treatment episodes. RESULTS In total, 107,331 units were transfused to 19,637 unique patients in 50,978 transfusion episodes. Most transfusions occurred in emergency settings, with 61.5% of use driven by emergency department admissions. The most common diagnoses were malignant neoplasms, anemias, and cardiovascular diseases. In total, 47.9% of transfusions were associated with a surgical procedure. Of these, 72.9% were for urgent surgery. Blood use fluctuated throughout the day, peaking in the early evening and being lowest during morning office hours. CONCLUSION The study offers a comprehensive picture of blood use in one of the largest European hospital organizations. In addition to elective use, a significant portion of blood demand is driven by urgent and emergency needs, which introduces some uncertainty in predicting blood use. Future studies should aim to understand both elective and emergency blood use to help improve demand estimates.

The authors have declared no competing interest.

This study was funded by the Finnish Red Cross Blood Service Research Fund and Government Research Funding (VTR).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The institutional review board at Helsinki University hospital granted a research and data permit for this study (HUS/579/2022, 17.10.2022). As the study is based purely on registry data, obtaining ethics committee approval was unnecessary pursuant to the Act on the Secondary Use of Health and Social Data (26.4.2019/552) in Finland.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes