Prehospital RhD risk, blood availability and the oxygen-delivery window
An evidence-informed analysis of emergency transfusion in females of childbearing potential, the balance between immediate survival and future reproductive risk, patient-selection physiology, and a testable question for future prehospital oxygen-delivery strategies.
What the current prehospital data establish.
The CREDIT-EMS cohort described civilian prehospital transfusion practice across 48 U.S. states between 2020 and 2024. It included 10,444 patients who received prehospital blood products. Among them, 1,589 were females of childbearing potential aged 12 to 50 years. A total of 957 of these 1,589 patients, approximately 60%, received at least one unit of RhD-positive whole blood or red blood cells.[1,2]
The frequency of RhD-positive exposure in this population increased substantially during the study period, from 43.2% in 2020 to 74.9% in 2024.[2]
Only 255 of 10,343 cases, 2.5%, had a prehospital interval of 20 minutes or less. Approximately 97.5% therefore remained in the prehospital care environment for more than 20 minutes.[2]
The future risk is low, but it is not zero.
Yazer, Vieni and Seheult modeled future hemolytic disease of the fetus and newborn, HDFN, after urgent prehospital RhD-positive transfusion in the 957 females identified by the earlier cohort. The maximum modeled HDFN rate for females of unknown RhD type was approximately 0.8%, occurring at ages 18 to 20 years. Across the modeled regional cohorts, the estimated future HDFN rate ranged from approximately 0.214% to 0.294% per year.[1]
The regional model was instantiated 500 times, representing approximately 2,500 simulated years. Across those simulations, 1,368 HDFN cases were calculated, or approximately 0.55 case per simulated year overall. The model incorporated region-specific age distributions, and historical prehospital transfusion volumes differed markedly by region, from 29 FCPs in the Northeast to 710 in the South per 5-year period. On that basis, the shortest modeled regional interval between HDFN cases was approximately 2.4 years and the longest approximately 80.7 years.[1]
These are model-derived regional population estimates. They are not observed clinical event intervals and they are not an individual patient's probability of HDFN. The authors concluded that future HDFN risk from urgent prehospital RhD-positive transfusion was low.[1] A 2026 narrative review similarly concluded that RhD-positive transfusion is supported when RhD-negative products are unavailable in hemorrhagic shock, while emphasizing risk mitigation and follow-up.[3]
The multidisciplinary 2026 joint position statement is even more explicit about the clinical trade-off. It reports D-alloimmunization rates after trauma transfusion in the range of approximately 8% to 43%, while modeled downstream severe HDFN or perinatal-death risks are substantially lower. Its conclusion is that life-saving transfusion should not be withheld when RhD-negative products are unavailable and transfusion is clinically indicated.[4]
The clinical logic is therefore not that the compatibility-related risk is unimportant. The logic is that the immediate risk of uncontrolled hemorrhage and inadequate resuscitation is greater.
The physiological problem begins before hospital arrival.
Severe hemorrhage can simultaneously reduce circulating volume, perfusion pressure and oxygen-carrying capacity. Whole blood and red blood cell transfusion are not only oxygen therapies, because whole blood also contributes volume and hemostatic components. However, restoration of oxygen-carrying capacity is one of the central physiological functions of red-cell-containing resuscitation.
The CREDIT-EMS median prehospital interval of 48 minutes, together with the finding that only 2.5% of cases had an interval of 20 minutes or less, shows that the prehospital phase can represent a substantial treatment window rather than a short transport interval.[2]
Ground EMS blood programs are also expanding. In June 2026 the Prehospital Blood Transfusion Coalition reported more than 400 U.S. 9-1-1 ground EMS agencies with blood transfusion programs.[5] JEMS reported the same milestone and noted that less than 3% of eligible agencies carried blood products.[6]
Pediatric consensus also points toward physiology, perfusion and clinical judgment.
Magill and colleagues convened a multidisciplinary panel of 20 experts in pediatric surgery, pediatric emergency medicine and EMS. The panel evaluated 208 candidate criteria across six voting rounds, and 35 recommendations reached the predefined threshold of at least 80% agreement.[7]
The proposed pediatric prehospital transfusion framework requires suspected severe hemorrhage, at least one sign of shock after first-line hemorrhage control, and EMS clinical judgment that transfusion is needed.[7]
Importantly, the assessment of shock was not limited to blood pressure. The consensus framework included poor perfusion, low cardiac output and validated pediatric shock indices. Routine use of end-tidal CO₂ as a transfusion trigger did not reach consensus.[7]
Emergency systems are managing several constraints at the same time.
The evidence can be separated into four linked problems:
- Time: hemorrhage and oxygen debt evolve before definitive hospital treatment.
- Availability: blood products cannot yet be positioned on most ground EMS units.[5,6]
- Compatibility: when RhD-negative products are unavailable, clinicians may accept a non-zero future alloimmunization risk rather than delay a clinically indicated transfusion.[1,3,4]
- Function and patient selection: the immediate objective is restoration of the physiological functions required to keep the patient alive, and emerging consensus supports using perfusion, shock physiology and clinical judgment rather than a single pressure threshold.[7]
This creates a useful research distinction. The goal should not be framed only as moving more donor blood closer to every patient. A broader systems objective is to determine how effective oxygen-carrying support can be made available earlier, while preserving the roles of hemorrhage control, donor blood, coagulation support, surgery and definitive hospital care.
A complementary prehospital design question.
Current blood-on-board programs demonstrate that prehospital clinicians need the capability to intervene before hospital arrival. They also expose the operational limits of relying exclusively on distributed donor-blood inventory.
A purified, non-RBC hemoglobin oxygen carrier would not contain intact donor erythrocytes and therefore would not be expected to create the same RhD antigen exposure pathway as RhD-positive donor red cells. That does not imply absence of other immunologic, vascular, renal, oxidative or product-specific risks. Those risks require independent evaluation.
If a Biological Hemoglobin Oxygen Carrier were validated for the relevant prehospital indication, with acceptable safety, efficacy, dosing, stability and operational characteristics, it could be investigated as a complementary bridge when immediate donor blood is unavailable, delayed or constrained by compatibility and logistics.
Based on the evidence reviewed here, we believe that the central prehospital challenge is not only blood availability or compatibility. It is the timely restoration of effective oxygen delivery. We believe that a validated room-temperature, long-shelf-life, non-RBC oxygen carrier could potentially reduce dependence of early prehospital oxygen-carrying support on donor-blood availability and conventional RBC ABO/RhD compatibility, while bridging selected patients to definitive transfusion and hospital treatment.
The hypothesis must be falsifiable, not promotional.
A future study should determine not only whether the product carries oxygen, but whether earlier availability changes clinically meaningful physiology and outcomes without introducing an unacceptable safety trade-off.
Internal evidence routes.
Primary literature and system sources.
- Yazer MH, Vieni C, Seheult JN. Rate of future hemolytic disease of the fetus and newborn following the prehospital transfusion of RhD-positive blood products to females of childbearing potential in the United States of America. Prehospital Emergency Care. Published online September 10, 2026. doi:10.1080/10903127.2026.2725214. PMID: 42664369.
- Rosen CL, Thomas SA, McCartin MP, et al. Characteristics, Regional Evaluation, and D-Antigen in Transfusions by Emergency Medical Services. JAMA Network Open. 2025;8(7):e2524368. doi:10.1001/jamanetworkopen.2025.24368.
- Murphy TO, Spinella PC, Young PP, et al.; THOR Network Foundation. RhD-Positive Transfusion in Females of Childbearing Potential in Hemorrhagic Shock: Risk, Reality, and Policy. Prehospital Emergency Care. Published online September 1, 2026. doi:10.1080/10903127.2026.2701877. PMID: 42441900.
- Henry R, Coleman JR, Holcomb JB, et al. Post-Transfusion Management of RhD-Negative Females of Childbearing Potential Who Receive RhD-Positive Low-Titer Group O Whole Blood and Red Blood Cells During Trauma Resuscitation: A Joint Position Statement and Resource Document. Journal of the American College of Surgeons. Published online July 22, 2026. doi:10.1097/XCS.0000000000002099. PMID: 42490058.
- Prehospital Blood Transfusion Coalition. Washington, DC: Over 400 Ground EMS Agency Blood Transfusion Programs. Institutional program update. June 23, 2026.
- JEMS. Ground EMS Blood Transfusion Programs Surpass 400 Agencies Nationwide. EMS industry report summarizing Prehospital Blood Transfusion Coalition data. June 22, 2026.
- Magill CF, Heintz H, Finney J, Nimmer M, Antevy PM, Clukies LD, Guyette FX, Ignacio RC, Kothari KM, Shah MI, Siegler JE, Studnek JR, Su J, Browne LR; Pediatric Prehospital Blood Transfusion Collaborative. Consensus Guidelines for Prehospital Transfusion in Children: A Modified Delphi Study. Prehospital Emergency Care. Published online September 11, 2026. doi:10.1080/10903127.2026.2729895. PMID: 42725789.