What is transfusion‑related acute lung injury (TRALI)?

What is TRALI (Transfusion-Related Acute Lung Injury)?

TRALI is a life-threatening complication of blood transfusion characterized by acute respiratory distress and noncardiogenic pulmonary edema occurring within 6 hours of transfusion, caused by either antibody-mediated or non-antibody-mediated mechanisms that trigger neutrophil activation and endothelial damage in the pulmonary vasculature 1, 2.

Clinical Definition and Diagnostic Criteria

TRALI presents as acute respiratory compromise with the following features:

• Timing: Onset during or within 6 hours after transfusion 3, 4
• Respiratory symptoms: Acute shortness of breath, hypoxemia
• Radiographic findings: Bilateral pulmonary infiltrates on chest imaging 3
• Pathophysiology: Noncardiogenic pulmonary edema (distinguishing it from volume overload) 2

The 2019 consensus redefinition eliminated the term "possible TRALI" and introduced two classifications 1:

• TRALI Type I: Occurs without pre-existing ARDS risk factors
• TRALI Type II: Occurs in patients with ARDS risk factors or mild existing ARDS

Importantly, TRALI remains a clinical diagnosis and does not require detection of white blood cell antibodies for confirmation 1.

Pathophysiology

TRALI develops through multiple potential pathways, but the common endpoint is neutrophil-mediated lung injury:

Primary Mechanisms:

Antibody-mediated (Immunogenic) TRALI: Most commonly caused by anti-HLA or anti-neutrophil antibodies in donor plasma, particularly from multiparous female donors who developed these antibodies during pregnancy 3, 5. These antibodies activate recipient neutrophils in pulmonary capillaries.

Non-antibody-mediated (Non-immunogenic) TRALI: Caused by biologically active lipids and other substances that accumulate during storage of blood products, which can directly activate neutrophils 3, 2.

The "Two-Hit" Hypothesis:

• First hit: Underlying patient condition (sepsis, surgery, inflammation) primes neutrophils 2
• Second hit: Transfusion delivers antibodies or bioactive lipids that trigger full neutrophil activation 2

The activated neutrophils release oxygen radicals and proteolytic enzymes that damage pulmonary endothelial cells, causing capillary leak and pulmonary edema 3.

Incidence and Risk

According to prospective surveillance data from 2009, TRALI occurs at a rate of 0.81 per 10,000 transfused blood components (8.1 per 100,000 components) 6. However, TRALI is widely believed to be underdiagnosed and underreported 5, 2.

Blood Products Implicated:

All plasma-containing blood products can cause TRALI, with the majority of cases linked to 2:

• Fresh frozen plasma (highest risk)
• Platelet concentrates
• Whole blood
• Packed red blood cells

Notably, albumin has not been implicated in TRALI reactions 5.

Clinical Presentation and Severity

TRALI varies significantly in severity 5:

• Can affect all age groups and both genders equally
• Ranges from mild respiratory distress requiring only supplemental oxygen to severe ARDS requiring mechanical ventilation
• Mortality can occur, though prognosis is substantially better than other causes of acute lung injury when appropriately managed 4, 2

Treatment Approach

Treatment is entirely supportive 3, 4, 2:

Respiratory Support:

• Mild cases: Nasal oxygen supplementation may suffice 3
• Severe cases: Mechanical ventilation with lung-protective strategies (as with ARDS)

Hemodynamic Management:

• Invasive hemodynamic monitoring in severe cases 3
• Critical caveat: Avoid diuretics - TRALI is noncardiogenic pulmonary edema, and diuretics are not beneficial and may worsen hemodynamics 3
• Judicious fluid management

Controversial Therapies:

• Glucocorticoid administration remains controversial with insufficient evidence 3

Prognosis:

Patients who survive the initial pulmonary insult have an excellent long-term prognosis 4, which distinguishes TRALI from other forms of acute lung injury.

Prevention Strategies

Since 2009, highly effective mitigation strategies have been implemented 3, 7:

Primary prevention: Use of plasma only from:

• Male donors
• Female donors without pregnancy history
• Female donors who test negative for HLA class I, II, and HNA antibodies

Impact: In Germany, since implementing these donor selection criteria in 2009, no TRALI-related deaths have been registered 3. Similar strategies in the United States and other countries have significantly reduced TRALI incidence 7, though it remains a leading cause of transfusion-associated mortality 8, 7.

Key Clinical Pitfalls

1. Misdiagnosis as volume overload (TACO): TRALI is noncardiogenic; giving diuretics worsens outcomes
2. Failure to report cases: All posttransfusion pulmonary edema should be reported to transfusion services for proper classification 1
3. Underrecognition: High clinical suspicion needed in any acute respiratory distress within 6 hours of transfusion