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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- If ANY adverse reaction during transfusion: STOP THE TRANSFUSION, keep IV access, call for help, recheck patient and unit identification
- Acute haemolytic reaction (ABO incompatibility): fever, rigors, hypotension, back/loin pain, dark urine, DIC — usually caused by clerical/identification error. Life-threatening emergency
- Febrile non-haemolytic reaction: commonest reaction (1-2%). Fever and rigors within 1-2 hours. Usually due to cytokine accumulation. Manage with paracetamol, slow/stop transfusion
- TRALI: non-cardiogenic pulmonary oedema within 6 hours — bilateral CXR infiltrates, hypoxia, NO raised JVP (unlike TACO). Supportive treatment, usually resolves within 72 hours
- TACO (transfusion-associated circulatory overload): pulmonary oedema from volume overload — raised JVP, hypertension. Slow rate, diuretics, sit upright
Overview
Blood transfusion reactions encompass a spectrum of adverse events occurring during or after transfusion of blood products. They range from common, mild febrile reactions to rare but life-threatening ABO-incompatible haemolytic transfusion reactions. The most important safety measure is correct patient identification and checking — the majority of serious haemolytic reactions result from human error at the bedside (giving the wrong unit to the wrong patient). All NHS hospitals have mandatory transfusion checking procedures and report serious adverse events to SHOT (Serious Hazards of Transfusion).
Epidemiology
Approximately 3 million units of blood components are issued in the UK annually. Febrile non-haemolytic reactions occur in 1-2% of transfusions. Allergic reactions occur in approximately 1-3% (mostly mild urticaria). TACO is the leading cause of transfusion-related mortality in the UK. TRALI has become rarer since the introduction of male-only plasma. Acute haemolytic reactions from ABO incompatibility are very rare (<1 in 100,000) but carry a mortality of 10-40%. Incorrect blood component transfused (IBCT) remains the most commonly reported near-miss/incident type in the SHOT annual report.
Clinical Features
Symptoms
Fever and rigors — commonest reaction (febrile non-haemolytic or early sign of haemolysis)
Urticaria, pruritus (allergic reaction — usually mild)
Back pain, loin pain (acute haemolytic reaction — intravascular haemolysis)
Dyspnoea, cough (TRALI, TACO, or anaphylaxis)
Chest tightness, wheeze (anaphylaxis)
Dark red/brown urine (haemoglobinuria — intravascular haemolysis)
"Sense of impending doom" (anaphylaxis or acute haemolysis)
Signs
Fever (>1°C rise from baseline)
Hypotension and tachycardia (haemolysis, anaphylaxis, or bacterial contamination)
Hypertension with raised JVP (TACO)
Bilateral crackles and hypoxia without raised JVP (TRALI)
Urticarial rash (allergic reaction)
Angioedema, bronchospasm, cardiovascular collapse (anaphylaxis)
DIC — oozing from venepuncture sites (severe acute haemolysis)
Investigations
First-line
STOP TRANSFUSION and recheck identityCheck patient wristband against blood unit label — MOST IMPORTANT first step. Clerical error is the commonest cause of ABO-incompatible transfusion
FBC, coagulation screen, U&Es, LFTsAssess for haemolysis (falling Hb) and DIC (prolonged PT/APTT)
DAT (direct Coombs test)Positive in immune-mediated haemolytic transfusion reaction
Second-line
LDH, haptoglobin, bilirubinHaemolysis markers: raised LDH, low haptoglobin, raised unconjugated bilirubin
Blood cultures (from patient AND from the unit)If bacterial contamination suspected (fever, rigors, hypotension)
Urine sampleHaemoglobinuria (red/brown urine) = intravascular haemolysis
Repeat group and crossmatchSend pre- and post-transfusion samples + the implicated unit to blood bank for investigation
CXRBilateral pulmonary infiltrates: TRALI (normal heart size, no effusions) vs TACO (cardiomegaly, effusions, upper lobe diversion)
BNP/NT-proBNPRaised in TACO (fluid overload/cardiac failure), NORMAL in TRALI — helps distinguish the two
Specialist
SHOT reportingAll serious transfusion reactions must be reported to SHOT (Serious Hazards of Transfusion) and the hospital transfusion team
1
Immediate actions for ANY reaction
- STOP the transfusion immediately
- Maintain IV access (flush with 0.9% saline)
- Check patient identity against the blood unit — exclude clerical error
- Observations: HR, BP, temp, SpO2, urine output
- Notify the blood bank and send samples for investigation
2
Febrile non-haemolytic reaction
- Paracetamol 1g
- Slow or stop transfusion depending on severity
- If settles within 30 minutes and no features of haemolysis: may cautiously restart at slower rate
- If rigors persist or temperature >39°C: stop transfusion, exclude haemolysis and bacterial contamination
3
Acute haemolytic reaction (ABO incompatibility)
- STOP transfusion — do NOT restart
- Aggressive IV fluid resuscitation (0.9% NaCl) to maintain urine output >100 mL/hour and prevent renal failure
- Send samples for investigation: DAT, repeat crossmatch, haemolysis screen
- Manage DIC if present (FFP, cryoprecipitate, platelets)
- Monitor renal function closely — may need renal support
4
TRALI
- Stop transfusion, high-flow oxygen, supportive care
- Manage as non-cardiogenic pulmonary oedema — may need CPAP or mechanical ventilation
- Do NOT give diuretics (unlike TACO — patient is not fluid overloaded)
- Usually resolves within 48-72 hours with supportive care
5
TACO
- Slow or stop transfusion, sit patient upright, give oxygen
- IV furosemide 20-40 mg — diuresis to relieve fluid overload
- Future transfusions: slower rate (1 unit over 3-4 hours), pre-transfusion furosemide, single unit prescribing
6
Allergic/anaphylaxis
- Mild urticaria: antihistamine (chlorphenamine 10 mg IV), may continue transfusion cautiously
- Anaphylaxis: IM adrenaline 0.5 mg (1:1000), ABC approach, do NOT restart transfusion
- IgA-deficient patients: at risk of anaphylaxis — need IgA-deficient or washed blood products
Complications
- Renal failure: From intravascular haemolysis (haemoglobinuria blocking renal tubules) — ABO incompatibility
- DIC: Triggered by ABO-incompatible haemolytic reaction
- Death: ABO incompatibility mortality ~10-40%. TACO is now the leading cause of transfusion-related death in the UK
- Delayed haemolytic reaction: Occurs 3-14 days post-transfusion — anamnestic antibody response. Falling Hb + positive DAT
- Iron overload: From chronic transfusion (each unit contains ~250 mg iron)
- Transfusion-transmitted infection: Now extremely rare in the UK due to rigorous screening
UKMLA Exam Tips
- 1FIRST action in ANY transfusion reaction: STOP THE TRANSFUSION + check identity
- 2ABO incompatibility = clerical error (giving wrong blood to wrong patient). Prevention = bedside checking procedure
- 3TRALI vs TACO: both cause pulmonary oedema. TRALI = normal JVP, normal BNP, bilateral infiltrates, do NOT give diuretics. TACO = raised JVP, raised BNP, GIVE diuretics
- 4TACO is now the leading cause of transfusion-related DEATH in the UK (not ABO incompatibility)
- 5IgA deficiency → anaphylaxis to blood products containing IgA → need IgA-deficient products or washed cells
- 6Febrile non-haemolytic reaction is the COMMONEST adverse reaction (1-2%) — give paracetamol, usually benign
practicetest your knowledge on blood transfusion reactionsApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — haematology and beyond.
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