5/18/2026
A 1,020-patient U.S. randomized trial found no significant survival difference between the two approaches — giving emergency teams flexibility to use whatever blood product is most available.
Whole blood and separated blood components are equally effective for treating severe traumatic hemorrhage before patients reach a hospital, according to a nationwide randomized trial led by University of Pittsburgh and UPMC clinicians and scientists. The findings were published May 18 in the New England Journal of Medicine and presented the same day at the American Thoracic Society annual meeting in Orlando.
Traumatic hemorrhage — uncontrolled bleeding from injury — is the leading cause of trauma death and the most time-sensitive emergency a person can face, more urgent than a stroke or heart attack.
Prehospital resuscitation is the practice of giving blood products to critically injured patients before they arrive at a hospital, typically during helicopter or ambulance transport. Donated blood is usually separated into components — red blood cells, plasma and platelets — for storage. Whole blood skips that step, delivering all three in a single unit. Both approaches have long been considered safe, but no large U.S. randomized trial had directly compared them in the field — until now.
About the TOWAR Trial
The TOWAR (Type O Whole Blood and Assessment of Age During Prehospital Resuscitation) trial enrolled 1,020 severely injured patients transported by medical helicopter to trauma centers from May 2022 to June 2025. It is among the largest prehospital blood transfusion studies ever conducted in the United States. Patients were randomized 2-to-1 to receive either whole blood or component therapy.
The whole blood used in the trial was low-titer group O whole blood, known as LTOWB — a Type O product with low antibody levels that can be safely given to any patient without prior blood-type crossmatching, making it practical for field use when a patient's blood type is unknown.
What the Trial Found
Thirty-day mortality was 25.9% among patients who received whole blood and 20.5% among those who received component therapy — a difference that was not statistically significant. Both rates compared favorably to an estimated one-third mortality rate among severely injured patients who do not receive prehospital blood transfusion, underscoring the life-saving potential of either approach.
"Traumatic bleeding is the leading cause of trauma death — it is preventable, and that starts with giving blood back to the injured person before they even arrive at the hospital," said co-lead author Jason Sperry, M.D., M.P.H., chief of trauma surgery at UPMC and Andrew B. Peitzman Professor of Surgery in Pitt's School of Medicine.
Co-lead author Francis Guyette, M.D., M.S., M.P.H., professor of emergency medicine in Pitt's School of Medicine and medical director of STAT MedEvac — the nation's largest academic, nonprofit critical care transport group, directed by a consortium of UPMC hospitals — said the result gives emergency teams real-world flexibility.
"It means that emergency responders can use whatever form of blood is most accessible to them," Guyette said. "In U.S. civilian emergencies, that may be component blood. In military settings, whole blood is often all that's available. We've shown that both are equally great options."
Blood Age Does Not Affect Outcomes
The trial also examined whether the age of donated blood affected patient outcomes. Whole blood is approved for use up to 21 days after donation. The TOWAR trial found no difference in outcomes between patients who received blood within 14 days of donation and those who received blood within the seven days before its expiration, confirming that whole blood remains effective throughout its full shelf life.
"Our approach allowed us to answer not only the question of whole blood versus component therapy, but also to evaluate the health impact of blood age," said senior author Stephen Wisniewski, Ph.D., professor of epidemiology and associate vice chancellor for clinical trials coordination at Pitt, and co-director of the Epidemiology Data Center at Pitt's School of Public Health. "Our trial provides reassurance by verifying current standards that support the use of whole blood units throughout their entire shelf life."
In March 2025, British researchers published results of the SWiFT trial in the New England Journal of Medicine, reporting that whole blood and blood components were similarly effective in front-line trauma care. The convergence of two independent, large randomized trials — one American, one British, both published in the same journal — is expected to inform updated guidelines from professional societies governing trauma surgery, emergency medicine and blood banking.
STAT MedEvac's air-medical network provided the prehospital enrollment infrastructure that enabled TOWAR to reach its nationwide scale, enrolling patients during active helicopter transports to trauma centers. The trial was funded in part by the U.S. Army Medical Research Acquisition Activity, reflecting a pipeline of military trauma research translated into civilian emergency medicine practice.
"We are hopeful that this study and future research will give emergency responders better tools to save lives," Guyette said.
Frequently Asked Questions
Q: What did the TOWAR trial find?
A: The trial found that whole blood and separated blood components were equally effective for treating severely injured patients before hospital arrival. Thirty-day mortality was 25.9% with whole blood and 20.5% with component therapy — a difference that was not statistically significant.
Q: Does it matter how old the donated blood is?
A: No. The trial found no difference in patient outcomes based on blood age — whether blood was transfused within 14 days of donation or within seven days of its 21-day expiration. Whole blood is safe and effective throughout its full shelf life.
Q: How do these findings affect civilian and military emergency teams?
A: Emergency teams can use whichever blood product is most accessible in their setting. Component blood is most common in U.S. civilian systems; whole blood is often the only option in military settings. The trial confirms both work equally well.
Additional Resources
- Published study: Prehospital Resuscitation with Type O Whole Blood for Trauma and Hemorrhage in the New England Journal of Medicine
- Press release: Nationwide trial: Whole blood and components equally effective in prehospital trauma care
- TOWAR Trial: TOWAR | LITES Network
- STAT MedEvac: STAT MedEvac
- American Thoracic Society 2026 Presentation (starts at 59:35): B83 AJRCCM/NEJM/JAMA CRITICAL CARE SESSION
- Multimedia (headshots): Jason Sperry, Frances Guyette, Stephen Wisniewski
Authors and Funding
Authors: Additional authors from Pitt, UPMC or both include James F. Luther, M.A.; Matthew D. Neal, M.D.; Mark H. Yazer, M.D.; Christian Martin-Gill, M.D.; Laura E. Vincent, M.S., R.N.; Ashley Harner, B.S.; and Bedda Rosario-Rivera, Ph.D. Other authors listed on the manuscript are from the University of Texas Health Science Center at Houston, University of Washington, University of Mississippi Medical Center, University of Cincinnati, MetroHealth Medical Center, University of Louisville, University of Alabama at Birmingham Health System, University of Manitoba and University of Tennessee Knoxville.
Funding and Disclosures: This research was supported by the Congressionally Directed Medical Research Program and the U.S. Army Medical Research Acquisition Activity under contract no. W81XWH-16-D-0024, task order W81XWH-20-F-0383 and R35GM119526.
