Overview
Blood transfusion, while life-saving, is not without risk. Transfusion reactions (TR) can occur during or after the procedure, ranging in severity from mild fever to fatal hemolysis, and every blood transfusion centre must maintain a record of all reported reactions.
Transfusion reactions are broadly classified as immunological or non-immunological, and further as immediate (within 24 hours) or delayed (days to months later). Understanding this classification, its causes, and the appropriate laboratory investigations is essential for safe transfusion practice and for correctly managing an affected patient.
Learning Objectives
After this lesson you will be able to…- Classify transfusion reactions as immunological/non-immunological and immediate/delayed
- Describe the pathogenesis of acute hemolytic transfusion reaction (AHTR)
- Explain febrile non-hemolytic, allergic, anaphylactic, and TRALI reactions
- Discuss delayed reactions including DHTR, post-transfusion thrombocytopenia, and GVHD
- List transfusion-transmitted infections and their standard screening methods
Clinical Story
Why This MattersTwenty minutes into a blood transfusion, a hospitalized patient develops sudden fever, chills, and lower back pain. The nursing staff immediately stops the transfusion and alerts the blood bank. The laboratory technologist must rapidly determine whether this represents a life-threatening acute hemolytic transfusion reaction from a clerical error, or a milder febrile non-hemolytic reaction — a decision that changes the entire management pathway.
Core Concepts
Transfusion reactions are classified as immunological or non-immunological, and each is further divided into immediate (occurring within 24 hours) or delayed (occurring days to months later). Immediate immunological reactions include acute hemolytic transfusion reaction, febrile non-hemolytic reaction, allergic and anaphylactic reactions, and TRALI. Immediate non-immunological reactions include septicemia and circulatory overload. Delayed immunological reactions include delayed hemolytic transfusion reaction, post-transfusion thrombocytopenia, and GVHD, while delayed non-immunological reactions include iron overload and transfusion-transmitted infections.
Intravascular AHTR occurs soon after transfusion, usually from ABO-incompatible blood, and is caused by complement activation leading to IgM-mediated red cell destruction within the circulation — a severe, life-threatening reaction. Causes are classified as clerical errors (incorrect patient/sample identification or labeling, wrong unit issued) or technical errors (blood grouping error, missed incompatibility on crossmatch, weak undetected antibodies, misinterpreted results). Investigations include checking for free hemoglobin/bilirubin pre- and post-transfusion, plasma haptoglobin, urine hemoglobin, a repeat direct antiglobulin test, and repeat compatibility testing.
FNHTR is a temperature rise of ≥1°C within 24 hours of transfusion due to alloimmunization to leucocyte/platelet antigens, preventable by leucoreduction. Allergic reactions arise from IgE on mast cells reacting with donor plasma proteins, causing urticaria; prevented by washed red cells. Anaphylactic reactions occur in IgA-deficient patients who have developed anti-IgA antibodies. TRALI results from donor granulocyte-specific and anti-HLA antibodies causing acute lung injury within 6 hours of transfusion, prevented by using leucocyte-depleted blood components.
Delayed hemolytic transfusion reaction (DHTR) occurs 2–10 days post-transfusion from an anamnestic antibody response to Rh, Kidd, Kell, or Duffy antigens, with red cells destroyed extravascularly by macrophages. GVHD results from donor T lymphocytes attacking an immunodeficient recipient, prevented by irradiating blood products. Delayed non-immunological complications include iron overload in chronically transfused patients and transfusion-transmitted infections such as HIV, Hepatitis B, Hepatitis C, syphilis, and malaria, all of which are screened for in every donated unit.
Laboratory Principle
Most immunological transfusion reactions occur because an antibody in the recipient (or occasionally the donor) recognizes a foreign antigen on transfused cells and triggers either direct complement-mediated lysis (as in acute hemolytic reaction), cytokine release from leucocyte/platelet antibody interaction (as in FNHTR), or an IgE-mediated hypersensitivity response (as in allergic and anaphylactic reactions). Non-immunological reactions instead arise from the physical, infectious, or metabolic burden that transfused blood places on the recipient's circulation and organs.
Equipment Required
Reagents & Materials
| Reagent / Material | Concentration / Grade | Purpose | Storage |
|---|---|---|---|
| Polyspecific AHG (Coombs) Reagent | Anti-IgG + Anti-C3d | Direct antiglobulin test pre/post transfusion | 2–8°C |
| Haptoglobin Assay Kit | Immunoturbidimetric | Detects intravascular hemolysis | As per manufacturer |
| ELISA Kits (HBsAg, Anti-HCV, Anti-HIV) | Commercial diagnostic kits | Transfusion-transmitted infection screening | 2–8°C |
| VDRL/TPHA Reagents | Standard serology reagents | Syphilis screening of donor units | 2–8°C |
Step-by-Step Procedure
At the first sign of a suspected reaction, stop the transfusion but keep the intravenous line open with saline.
Recheck the patient's identification against the blood bag label to rule out a clerical error as the cause.
Draw fresh blood and urine samples from the patient for comparison with the pre-transfusion sample.
Examine plasma/urine for free hemoglobin, measure haptoglobin, repeat the direct antiglobulin test, and repeat compatibility testing against the donor bag.
Record all findings in the transfusion reaction register and notify the treating physician and blood bank in-charge.
Flow Diagram
Quality Control
Every suspected transfusion reaction must trigger a standardized reaction work-up including repeat ABO/Rh typing, direct antiglobulin test, and visual inspection of post-transfusion plasma for hemolysis, with results documented against a checklist to ensure no step is missed.
Hemovigilance programs at regional or national level collect transfusion reaction data from participating blood banks, allowing benchmarking of reaction rates and identification of systemic issues in blood collection, processing, or administration practices.
Reference Values
Normal Ranges⚠️ Reference ranges may vary between laboratories. Always apply your laboratory's established reference intervals.
Clinical Interpretation
| Finding | Possible Significance | Action / Follow-up |
|---|---|---|
| Fever + back pain + hemoglobinuria during transfusion | Acute hemolytic transfusion reaction — likely ABO incompatibility | Stop transfusion immediately; full reaction work-up; notify physician urgently |
| Isolated fever without hemolysis markers | Febrile non-hemolytic transfusion reaction | Antipyretics; slow or stop transfusion per protocol; continue monitoring |
| Acute dyspnea and hypoxia within 6 hours | Suspected TRALI | Stop transfusion; supportive respiratory care; test donor for anti-HLA/granulocyte antibodies |
Common Errors & How to Avoid Them
Cause: Continuing a transfusion after early reaction symptoms appear worsens the severity of hemolysis or anaphylaxis.
Prevention: Train ward staff to stop transfusion immediately at the first sign of any reaction and keep the line open with saline.
Cause: Delayed sample collection may miss transient free hemoglobin or allow it to clear, giving a false-negative hemolysis work-up.
Prevention: Collect post-reaction blood and urine samples as soon as possible after the reaction is recognized.
Cause: Assuming a benign febrile reaction without checking for hemolysis markers can delay recognition of a life-threatening AHTR.
Prevention: Always perform the full reaction investigation panel (DAT, haptoglobin, repeat crossmatch) for any febrile reaction during transfusion.
Laboratory Tips from the Bench
Leucoreduced blood components dramatically reduce the incidence of febrile non-hemolytic transfusion reactions and are recommended for patients receiving multiple transfusions.
Always check the blood bag label against the patient's wristband at the bedside immediately before transfusion — this single step prevents the majority of ABO-incompatible acute hemolytic reactions.
Remember TRALI by its timing: 'Trouble breathing, Rapid onset, ALI within 6 hours' — helping distinguish it from circulatory overload, which develops more gradually.
Important Notes
The majority of acute hemolytic transfusion reactions result from clerical errors — incorrect patient identification or sample/bag labeling — not laboratory technical failures, underscoring the importance of bedside verification.
Irradiating cellular blood products before transfusion to immunodeficient patients inactivates donor T lymphocytes, effectively preventing graft-versus-host disease.
Interactive Quiz
Test Your KnowledgeFlashcards
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Clinical Case Study
Apply Your KnowledgeTwenty minutes into a packed red cell transfusion following surgery, the patient develops fever, rigors, and lower back pain. The nursing staff immediately stops the transfusion.
The discrepancy between the patient's true group (O positive) and the transfused unit's label (A positive) confirms an ABO-incompatible transfusion due to a clerical identification error, explaining the acute intravascular hemolysis.
- →A mismatch between patient blood group and transfused unit group confirms a clerical, not technical, error.
- →Hemolysis markers (pink plasma, positive DAT) must always be checked in any suspected transfusion reaction.
- →Bedside identity verification immediately before transfusion is the last line of defense against this type of error.
Frequently Asked Questions
A suspected reaction should be reported to the blood bank immediately once the transfusion is stopped, as prompt investigation is essential to distinguish life-threatening reactions from milder ones and to guide safe management of any subsequent transfusion.
Not entirely, but strict adherence to identification protocols, leucoreduction, washed/irradiated components where indicated, and thorough pretransfusion compatibility testing dramatically reduces both the frequency and severity of reactions.
In malaria-endemic regions, the parasite can survive in stored blood and be transmitted to a recipient via transfusion, so screening donor blood for malaria antigen is part of the standard infectious disease panel in those areas.
Quick Revision
10-Minute ReviewKey Takeaways
- Transfusion reactions range from mild fever to fatal hemolysis and must always be taken seriously.
- Immediate immunological reactions include AHTR, FNHTR, allergic, anaphylactic, and TRALI reactions.
- Delayed immunological reactions include DHTR, post-transfusion thrombocytopenia, and GVHD.
- Non-immunological reactions include septicemia, circulatory overload, iron overload, and transmitted infections.
- Clerical errors remain the leading preventable cause of acute hemolytic transfusion reactions.
- A standardized investigation panel (DAT, haptoglobin, repeat crossmatch) should follow every suspected reaction.
Competency Checklist
Track Your MasteryReferences
- National Institute of Open Schooling. Hematology and Blood Bank Technique, Lesson 14: Transfusion Reactions.
- AABB Technical Manual. 20th ed. American Association of Blood Banks.
- Hoffbrand AV, Moss PAH. Essential Haematology. 7th ed. Wiley-Blackwell.