Transfusion-Related Acute Lung Injury (TRALI) and Transfusion-Associated Circulatory Overload (TACO)

TRALI and TACO are the two major pulmonary complications of transfusion and together rank among the leading causes of transfusion-related death. TRALI is acute, non-cardiogenic pulmonary edema occurring during or shortly after transfusion, attributed to donor antileukocyte antibodies or biologically active lipids activating recipient neutrophils. TACO is cardiogenic pulmonary edema from volume overload. Distinguishing the two is central to transfusion safety because they differ in mechanism and prevention.

Definition

TRALI is acute hypoxemia with non-cardiogenic bilateral pulmonary edema arising within about six hours of transfusion, whereas TACO is acute pulmonary edema due to circulatory volume overload from the transfused component; both present as transfusion-associated respiratory distress but differ in mechanism.

Scope

This entry covers the definitions, mechanisms, and distinguishing features of TRALI and TACO, the two-hit model of TRALI pathogenesis, and the role of donor-related factors. It is a reference description of these entities and their pathophysiology, not bedside diagnostic or treatment guidance.

Key concepts

• Non-cardiogenic pulmonary edema
• Donor anti-HLA and anti-HNA antibodies
• Two-hit model of TRALI
• Neutrophil priming and activation
• Cardiogenic (hydrostatic) pulmonary edema
• Circulatory volume overload
• TRALI versus TACO differentiation
• Mitigation through donor selection

Mechanisms

In the predominant antibody-mediated form of TRALI, donor plasma contains antibodies against recipient human leukocyte (HLA) or human neutrophil (HNA) antigens; these activate primed neutrophils sequestered in the pulmonary microvasculature, increasing vascular permeability and causing non-cardiogenic edema. A widely used two-hit model holds that an underlying inflammatory condition primes neutrophils (first hit) before a transfusion-borne factor — antibodies or biologically active lipids — triggers injury (second hit). TACO, by contrast, is hydrostatic edema from circulatory overload when the transfused volume exceeds what the recipient's cardiovascular system can accommodate. Semple, Rebetz, and Kapur review the pathophysiology of both, and Toy and colleagues provide the consensus definition of TRALI.

Clinical relevance

Separating TRALI from TACO and from other causes of post-transfusion respiratory distress is a core concept underlying transfusion safety measures such as preferential use of plasma from donors at low risk of carrying leukocyte antibodies. This entry describes the entities and mechanisms for reference; it does not provide diagnostic criteria, monitoring, or treatment recommendations for individual patients.

Epidemiology

TRALI and TACO have repeatedly appeared among the leading reported causes of transfusion-related mortality in hemovigilance data. Mitigation strategies for TRALI, such as using plasma from male or never-pregnant donors, have been associated with reductions in reported cases. Vamvakas and Blajchman discuss these as principal causes of transfusion-related death, and SHOT reporting (Bolton-Maggs and Cohen) tracks their incidence and the effect of mitigation.

History

Pulmonary reactions to transfusion were described for decades before the entity was formalized; the term TRALI and a consensus definition were established in the 2000s, with the Toy and colleagues review reflecting that consensus framework. Recognition that female donors with pregnancy-induced leukocyte antibodies contributed disproportionately to cases led to donor-management strategies, while TACO gained prominence as infectious and other immune risks declined.

Debates

How reliably can TRALI be distinguished from TACO?

The two share the presentation of acute transfusion-associated pulmonary edema but differ mechanistically (permeability versus hydrostatic), and overlapping features mean that classification can be difficult, which affects both reporting and prevention strategies.

Seminal works

• toy-2005
• semple-2019

Frequently asked questions

What is the difference between TRALI and TACO?

TRALI is non-cardiogenic pulmonary edema caused by an immune or biological insult that increases pulmonary vascular permeability, whereas TACO is cardiogenic edema caused by circulatory volume overload; both cause respiratory distress after transfusion but differ in mechanism and prevention.

What is the two-hit model of TRALI?

It proposes that a predisposing inflammatory state first primes neutrophils sequestered in the lungs, and a transfusion-borne factor such as anti-leukocyte antibodies or bioactive lipids then activates them, producing acute lung injury.