Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
TRALI, TACO and severe allergic transfusion reactions
Haematology and transfusion · UK scope · Sources checked 27 Aug 2026 · Clinical review pending
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Breathlessness, hypoxia or collapse during transfusion
TRALI, TACO and anaphylaxis can look similar initially; stop exposure and treat airway, breathing and circulation before waiting for a definitive label.
Action: Stop the component, maintain intravenous access with 0.9% sodium chloride through new tubing, call for senior and critical-care help and assess ABCDE. Give high-concentration oxygen and monitor continuously. For anaphylaxis give intramuscular adrenaline 500 micrograms into the anterolateral thigh and repeat after 5 minutes if airway, breathing or circulation problems persist. Sit an overloaded patient upright and give intravenous loop diuretic with ventilatory support; use supportive oxygen or ventilation for TRALI and avoid reflex diuresis unless hydrostatic overload also exists. Notify the transfusion laboratory immediately.
Overview
Differentiate the principal respiratory transfusion emergencies, deliver syndrome-specific oxygen, diuresis or adrenaline and preserve evidence for transfusion investigation.
TRALI is acute hypoxaemic lung injury with pulmonary oedema on imaging arising during or within six hours of transfusion. Respiratory status should have been stable or improving beforehand, and left-atrial hypertension must not be the main explanation. A recipient inflammatory state can prime pulmonary neutrophils, followed by donor antibodies or biological mediators that activate them and injure endothelium. Fever, hypotension and transient leucopenia can occur. Plasma-rich components are commonly implicated, but any component containing plasma can be associated.
Treat TRALI supportively. Give oxygen, use lung-protective invasive ventilation if needed and seek critical-care help early. Conservative fluid practice may be appropriate after perfusion is secure, but diuretics do not reverse permeability oedema and can worsen hypotension. Send acute-reaction tests and assess cardiac evidence because TRALI and TACO can overlap. The transfusion service reports the case and coordinates donor antibody investigation and withdrawal of associated products; the clinical team should not contact or speculate about individual donors.
Practice
Two practice questions
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Haematology and transfusionOriginal SBA
Pulmonary oedema after transfusion
A patient with chronic kidney disease becomes breathless and hypertensive two hours after a second red-cell unit. Examination shows raised JVP and basal crackles. What is the most likely reaction?
Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources
Sources and review status
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem ·
TACO results from hydrostatic overload and is reportable even when other fluids or cardiac disease contributed. SHOT surveillance uses respiratory compromise or pulmonary oedema during or up to 12 hours after transfusion with additional cardiovascular, fluid-overload or biomarker evidence. Orthopnoea, basal crackles, raised JVP, hypertension, peripheral oedema and an S3 support it. Chest imaging may show cardiomegaly, septal lines and effusions; echocardiography and a post-to-pre natriuretic peptide change can support but not independently prove causation.
Treat TACO by stopping transfusion, sitting the patient upright, giving oxygen and administering an intravenous loop diuretic when clinically appropriate. Use CPAP or invasive support if pulmonary oedema is severe and manage precipitating arrhythmia or cardiac ischaemia. Prevention is more effective than rescue: complete a pretransfusion risk assessment, challenge the indication, use single-unit or weight-based prescribing, avoid unnecessarily rapid administration, review concurrent fluids and reassess before another unit. A routine prophylactic diuretic for everyone is not evidence-based and can injure a hypovolaemic patient.
Severe allergic transfusion reaction spans angioedema and bronchospasm to anaphylactic shock. Diagnose anaphylaxis when sudden airway, breathing or circulation compromise occurs, usually with skin or mucosal changes but sometimes without them. Stop the component and give intramuscular adrenaline 500 micrograms using 1 mg/mL solution into the anterolateral thigh; repeat after five minutes if problems persist. Lay the hypotensive patient flat with legs raised unless breathing requires position adjustment, avoid sudden standing and give rapid crystalloid boluses with repeated response assessment.
Adrenaline is time critical. Antihistamines and corticosteroids do not replace it and must not delay it. Intravenous adrenaline has a high dosing-error and arrhythmia risk and belongs only in expert hands with continuous monitoring, typically as a titrated infusion for refractory shock. In pregnancy, give intramuscular adrenaline at the standard adult dose, position with left uterine displacement and involve obstetric, anaesthetic and neonatal teams. After recovery, observe according to severity, treatment and risk of biphasic reaction under the current RCUK pathway.
Key points
First-line shared action is stop the transfusion, keep access with new saline tubing, perform ABCDE and contact the transfusion laboratory.
TRALI causes non-cardiogenic pulmonary oedema during or within six hours, with hypoxaemia and bilateral infiltrates not mainly explained by hydrostatic pressure.
TRALI often features fever or hypotension with normal or low JVP; treat with oxygen and lung-protective ventilatory support, not routine diuresis.
TACO causes hydrostatic pulmonary oedema during or up to 12 hours after transfusion, supported by hypertension, raised JVP, positive balance, cardiomegaly, natriuretic-peptide rise and response to diuresis.
First-line TACO treatment is stop transfusion, sit upright, give oxygen, assess for intravenous loop diuretic and escalate to CPAP or critical care when necessary.
Prevent TACO by verifying indication, prescribing one unit or weight-adjusted volume, using an appropriate slower rate and reassessing before further components.
Anaphylaxis is defined clinically by sudden airway, breathing or circulation compromise; skin or mucosal change supports it but can be absent.
First-line anaphylaxis medicine is intramuscular adrenaline 500 micrograms from 1 mg/mL solution into the anterolateral thigh, repeated after five minutes if needed.
Give rapid intravenous crystalloid for anaphylactic shock, call the resuscitation team and use intravenous adrenaline only in an expert monitored setting.
Aetiology
01
TRALI donor and recipient interaction
Donor anti-HLA or anti-neutrophil antibodies and biologically active mediators can activate primed recipient neutrophils, although some cases occur without a demonstrable donor antibody.
02
TACO from excessive circulatory load
Rapid, high-volume or unnecessary transfusion exceeds cardiovascular and renal capacity, especially with heart failure, kidney dysfunction, positive balance, low weight or severe chronic anaemia.
03
Allergic plasma-protein exposure
Recipient hypersensitivity to donor plasma proteins produces urticaria through to systemic anaphylaxis; IgA deficiency with anti-IgA explains only a minority of severe recurrent reactions.
04
Mixed and competing causes
Sepsis, haemorrhage, aspiration, baseline ARDS and fluid resuscitation can coexist with transfusion and create overlapping TRALI, TACO or allergic physiology.
Pathophysiology
1
TRALI permeability oedema
Activated pulmonary neutrophils injure capillary endothelium, allowing protein-rich fluid into alveoli and causing acute hypoxaemia without left-atrial hypertension as the main driver.
2
TACO hydrostatic oedema
Intravascular volume and pressure rise faster than the circulation can accommodate, increasing pulmonary capillary hydrostatic pressure and producing cardiogenic interstitial and alveolar fluid.
3
Anaphylactic mediator release
Mast-cell and basophil mediators cause vasodilation, capillary leak, bronchoconstriction and airway oedema, so shock or obstruction can progress before skin signs appear.
4
Transfusion as a temporal trigger
Symptoms developing during or soon after a component establish a safety signal but not causality; phenotype, timing and alternative disease determine final haemovigilance classification.
Clinical features and red flags
TRALI phenotype
Hypoxaemia and bilateral non-cardiogenic pulmonary oedema during or within six hours, often with fever or hypotension, and no dominant hydrostatic cause.
TACO phenotype
Orthopnoea, hypertension, raised JVP, crackles and positive balance during or within 12 hours, often improving with diuresis.
Anaphylaxis phenotype
Sudden airway swelling, wheeze, hypoxaemia, hypotension or collapse, with or without urticaria, demands immediate intramuscular adrenaline.
Mild allergy
Pruritus or limited urticaria without airway, breathing or circulation involvement remains mild but must be watched for progression.
Mixed pulmonary reaction
A patient with inflammation and fluid overload may meet overlapping TRALI and TACO features; supportive care and formal classification address both.
Red flags requiring action
Stridor, tongue or airway swelling, wheeze, persistent hypotension or collapse indicates anaphylaxis even when urticaria is absent.
New hypoxaemia with bilateral pulmonary oedema during or within six hours of transfusion and no dominant left-atrial hypertension suggests TRALI.
Dyspnoea, orthopnoea, hypertension, raised JVP and positive fluid balance during or up to 12 hours after transfusion suggests TACO.
Investigations
01First-line: clinical phenotype and fluid balanceFirst stepFirst line
Why
Separate airway allergy, permeability oedema and hydrostatic overload quickly.
Interpretation and limitations
Document JVP, blood pressure, crackles, oedema, rash, wheeze, temperature, all fluid, component volume and response to position or diuresis.
02Pulse oximetry, blood gas and chest imaging
Why
Measure respiratory failure and confirm pulmonary oedema.
Interpretation and limitations
Bilateral infiltrates support TRALI or TACO; cardiomegaly, effusions and septal oedema favour hydrostatic overload but are not individually diagnostic.
03ECG, natriuretic peptide and echocardiography
Why
Assess cardiac strain, rhythm, ischaemia and left-sided filling pressure.
Interpretation and limitations
Elevated or rising BNP or NT-proBNP and impaired cardiac function support TACO; critical illness and renal failure reduce specificity.
04Acute transfusion reaction screen
Why
Exclude haemolysis, incompatibility and contaminated-component sepsis.
Interpretation and limitations
Repeat group, DAT, haemolysis markers and cultures as symptoms dictate; respiratory signs do not rule out another simultaneous reaction.
Differential diagnosis
01
Acute haemolysis or contaminated component
Fever, rigors and shock with pain, dark urine or identity discrepancy suggest haemolysis, while high fever and collapse require patient and component cultures for bacterial sepsis.
02
Cardiogenic failure unrelated to transfusion
Acute coronary syndrome, arrhythmia, renal failure or excessive crystalloid may explain pulmonary oedema but does not remove the need to report a temporally related TACO event.
03
Pulmonary embolism, aspiration or pneumonia
Focal imaging, aspiration history, thrombotic risk or infection can produce hypoxaemia; several causes may coexist and require parallel investigation.
04
Mild isolated allergic reaction
Localised urticaria or pruritus without airway, breathing or circulatory compromise is not anaphylaxis, although progression requires continued observation and reassessment.
Additional chapter-specific clues
Alternative serious reaction
High fever, rigors, pain, dark urine or identity discrepancy directs parallel evaluation for sepsis and haemolysis rather than isolated respiratory classification.
Management
01Acute respiratory reactionStop and phenotype while supporting ABCFirst stepBreathlessness, hypoxia, wheeze or collapse begins during or shortly after transfusion.+
1Stop the component, maintain access through new tubing, give oxygen, call senior help and notify the transfusion laboratory.
2Look immediately for airway swelling, wheeze, rash, JVP, hypertension, fever, fluid excess, pain and dark urine.
3Treat anaphylaxis, TACO or TRALI physiology immediately while sending reaction tests and imaging; do not await a final label.
02Suspected TRALISupport non-cardiogenic lung injuryHypoxaemia and bilateral oedema arise within six hours without hydrostatic pressure as the main driver.+
1Provide oxygen and early critical-care review, using lung-protective ventilation when required.
2
Complications
01
Respiratory failure
TRALI and TACO can require non-invasive or invasive ventilation; severe hypoxaemia may progress rapidly after the component is stopped.
02
Cardiac arrest and organ hypoperfusion
Anaphylactic vasodilation, TACO-related failure or profound hypoxaemia can cause peri-arrest physiology, renal injury, myocardial injury and neurological harm.
03
Recurrent preventable reaction
Failure to document TACO risk, severe allergy or implicated donor investigation can expose the patient or another recipient to a repeat event.
04
Unnecessary future transfusion avoidance
An imprecise label can deny necessary blood or drive inappropriate specialised components; expert classification enables proportionate prevention rather than blanket exclusion.
Monitoring and follow-up
Use continuous oxygen saturation, ECG and frequent blood pressure and respiratory assessment during acute respiratory or allergic instability.
In TACO, chart urine output, cumulative fluid balance, weight where feasible, renal function and electrolytes after diuresis.
In TRALI, trend oxygen requirement, gas exchange and ventilator parameters and reassess for cardiac overload or an alternative ARDS trigger.
After adrenaline, monitor airway, breathing, perfusion and recurrence; determine observation duration from reaction severity, repeat doses and RCUK risk factors.
Review chest imaging, ECG, natriuretic peptides, echocardiography, tryptase and acute-reaction results in their timing and clinical context.
Document and report the event, update special requirements and ensure the patient, GP and future transfusion teams receive clear prevention advice.
Special situations
Timing separates imperfectly
TRALI is defined within six hours and TACO can present up to 12 hours, but early TACO and mixed events remain common diagnostic challenges.
Blood pressure is a useful clue
Hypertension supports TACO while hypotension is more typical of TRALI or anaphylaxis, although treatment and comorbidity can blur the pattern.
Skin signs are optional
Anaphylaxis can present with isolated shock or bronchospasm, so absence of urticaria must not delay intramuscular adrenaline.
Diuresis is a diagnostic clue
Rapid improvement after loop diuretic supports hydrostatic overload but does not prove transfusion causation or exclude coexisting lung injury.
TRALI is a donor-safety event
Prompt transfusion-service notification allows investigation of the implicated donor and other components that may protect additional recipients.
TACO begins at prescription
Many episodes are preventable through indication review, single-unit dosing, weight awareness, rate selection and post-unit reassessment.
Common pitfalls
01
Do not continue or merely slow a component when acute breathlessness or collapse occurs.
02
Do not delay intramuscular adrenaline for antihistamine, steroid, tryptase sampling or intravenous access.
03
Do not use subcutaneous adrenaline or an unmonitored intravenous bolus for routine anaphylaxis treatment.
04
Do not require urticaria before diagnosing anaphylaxis.
05
Do not give routine diuretic for suspected TRALI without evidence of hydrostatic overlap.
06
Do not assume all pulmonary oedema after transfusion is TACO or all hypotensive oedema is TRALI.
07
Do not diagnose TACO from a raised natriuretic peptide alone in renal failure or critical illness.
08
Do not resume transfusion after a severe respiratory reaction without specialist reassessment and a new plan.
A mild isolated rash may respond to an antihistamine after stopping and assessment, but antihistamines do not treat airway compromise or shock.
Chest radiography, blood gas, ECG, fluid balance, cardiac assessment and natriuretic peptides help distinguish TACO from TRALI but no single test is a gold standard.
Return the implicated component, complete reaction samples and document timing, volume, rate and total fluid because classification drives donor and future-recipient safety.
Severe chronic anaemia, low body weight, cardiac or renal impairment and multiple rapid components create a high-risk TACO phenotype requiring prevention before transfusion starts.
Fever, rigors, shock, pain or haemoglobinuria widens the emergency differential to contaminated component and acute haemolysis and requires cultures and compatibility investigation.
05Serum tryptase
Why
Support mast-cell activation after suspected anaphylaxis.
Interpretation and limitations
Take timed samples under the local pathway without delaying adrenaline; a normal result does not exclude clinical anaphylaxis and a baseline may be needed later.
06Donor and immunological investigation
Why
Define preventable TRALI or recurrent severe allergy after stabilisation.
Interpretation and limitations
The transfusion service coordinates donor HLA or HNA work and selected IgA or anti-IgA testing; results guide future components rather than acute resuscitation.
AlternativeAvoid routine loop diuretic when perfusion is low and hydrostatic overload is unsupported; investigate overlap and alternative lung injury.
3Report urgently to the transfusion service for haemovigilance classification and donor or co-component investigation.
03Suspected TACOUnload the circulationRespiratory oedema with hypertension, raised JVP or positive balance occurs within 12 hours.+
1Stop transfusion, sit upright, give oxygen and an intravenous loop diuretic selected for previous exposure and renal function.
2Use CPAP or critical care for severe pulmonary oedema and treat cardiac or renal precipitants.
3Record the reaction and create a future one-unit, weight, rate and fluid-risk plan before any further transfusion.
04Severe allergy or anaphylaxisGive adrenaline firstSudden airway, breathing or circulation compromise occurs with or without skin signs.+
1Give intramuscular adrenaline 500 micrograms into the anterolateral thigh and repeat after five minutes if ABC problems persist.
2EscalationCall the resuscitation team, give high-flow oxygen and rapid crystalloid boluses, positioning safely; escalate refractory shock to expert adrenaline infusion.
3After recovery, obtain indicated tryptase samples and specialist evaluation and plan washed or other components only according to the established mechanism.
05TACO preventionPrescribe the patient, not the packPretransfusion assessment identifies cardiac, renal, weight, balance or chronic-anaemia risk.+
1Reconfirm the component indication and whether a non-transfusion treatment can provide benefit safely.
2Use one unit or weight-adjusted volume, an appropriate slower rate and a documented monitoring plan; rationalise other fluids.
3Reassess symptoms, observations, fluid state and laboratory response before authorising more and individualise any diuretic.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
First-line life-saving treatment for transfusion-associated anaphylaxis through vasoconstriction, bronchodilation and reduction of mucosal oedema.
Adrenaline for anaphylaxis
Give 500 micrograms intramuscularly using 0.5 mL of 1 mg/mL adrenaline into the anterolateral thigh; repeat after 5 minutes if airway, breathing or circulation compromise persists while expert help is mobilised.
Do not delay for intravenous access, antihistamine or steroid. Intravenous bolus adrenaline risks fatal dosing error and arrhythmia and is for appropriately experienced specialists in a monitored setting. Use the same IM dose in pregnancy with left uterine displacement and urgent obstetric support.
Reduces hydrostatic pulmonary congestion in TACO after transfusion has been stopped and position and oxygen addressed.
Furosemide for TACO
Give 20 to 40 mg intravenously initially in a loop-diuretic-naive adult with clinically supported overload, then reassess urine output, blood pressure and respiratory response; a patient already taking loop diuretic commonly needs at least an equivalent or higher intravenous dose under the acute-heart-failure plan.
Individualise for prior dose, renal function, frailty and blood pressure. Monitor potassium, sodium, creatinine and urine output. Do not give reflexively for TRALI or anaphylactic shock, where intravascular depletion and hypotension may worsen.
09
Do not request washed or CMV-negative components indiscriminately; match future modification to the confirmed reaction mechanism.