Risk of Reactions During Blood Transfusion
Allergic reactions occur in approximately 1-3% of all blood transfusions, with severe anaphylactic reactions occurring much less frequently at approximately 1 in 30,000 transfusions. 1, 2
Overall Reaction Rates
The risk of any transfusion reaction varies by type and severity:
- Allergic reactions occur in 1 in 2,338 to 1 in 4,124 transfusion episodes, representing approximately 17% of all reported transfusion reactions 1
- Severe allergic reactions (anaphylaxis/anaphylactoid) occur in approximately 1 in 30,000 transfusions, or 7.7% of all allergic reactions 1
- Febrile non-hemolytic reactions occur in 1.1-2.15% of transfusions depending on leukoreduction 3
- TACO (Transfusion-Associated Circulatory Overload) is now the most common cause of transfusion-related mortality and major morbidity, occurring in 1-8% of patients 4, 3
- TRALI (Transfusion-Related Acute Lung Injury) occurs at 8.1 per 100,000 transfused components 3
Product-Specific Risks
Different blood products carry varying allergic reaction risks:
- Platelet transfusions have the highest rate of allergic reactions among blood components, with rates up to 5.5% for unmanipulated apheresis platelets 4, 5
- Plasma-containing products (FFP, platelets) more commonly cause allergic reactions compared to red blood cells 4
- Red blood cells typically cause febrile-type reactions rather than allergic reactions 4
High-Risk Patient Populations
Patients with previous reactions face substantially elevated risk:
- History of allergic transfusion reactions: These patients have a median of 6 transfusions before first reaction, but this increases with plasma-reduced products 5
- IgA deficiency: Patients with selective IgA deficiency are at higher risk for severe anaphylactic reactions 6
- Multiple transfusion history: Repeated transfusions increase sensitization risk 6
Critical Monitoring Requirements to Detect Reactions Early
All patients require standardized vital sign monitoring regardless of reaction history to detect reactions promptly:
- Baseline assessment within 60 minutes before starting transfusion 4, 7
- 15-minute check after starting each unit—this is the critical window when most reactions manifest 4, 7
- Final assessment within 60 minutes of completion 4, 7
- Respiratory rate is the most critical vital sign, as dyspnea and tachypnea are early indicators of serious reactions including TRALI and anaphylaxis 4, 7
Special Considerations for Patients with Allergy History
For patients with documented previous allergic transfusion reactions, several strategies reduce recurrence risk:
- Plasma reduction through concentrating apheresis platelets reduces allergic reactions by 73% (from 5.5% to 1.7%) 5
- Washed blood products reduce allergic reactions by 95% for platelets (to 0.5%) and 89% for RBCs (to 0.3%) 5
- Premedication with acetaminophen and antihistamines is commonly used but has failed to prevent reactions in controlled studies and may mask early warning signs 8
- Avelumab (an immunotherapy agent, not blood product) requires premedication with acetaminophen and antihistamine due to 25% infusion reaction rate, but this does not apply to standard blood transfusions 4
Important Clinical Pitfalls
Several common practices should be avoided:
- Do not use steroids and antihistamines indiscriminately as routine premedication—current evidence shows they are ineffective at preventing reactions and may suppress immunity in immunocompromised patients 4, 8
- Do not attribute symptoms to other causes without considering transfusion reaction—maintain high clinical suspicion 9
- Do not restart transfusion even if mild symptoms improve, as reactions may progress with continued exposure 9
- Distinguish between TACO and TRALI: TACO requires diuretics while TRALI is contraindicated for diuretics—this distinction is critical as both present with respiratory distress 4, 9
Personalized Approach Based on Reaction History
The current recommendation is a tailored approach based on symptoms rather than blanket premedication 4: