Question 43 A blood transfusion reaction may occur _________ hours post-transfusion.
Blood transfusion reactions can occur from immediately (acute, within minutes) up to 24 hours post-transfusion for acute reactions, or even days to weeks later for delayed reactions.
The classic exam answer is: a blood transfusion reaction may occur up to 24 hours post-transfusion (for acute hemolytic and other immediate reactions).
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Answer
The standard exam answer is 24 hours.
Transfusion reactions are classified by timing:
| Category | Timing | Examples |
|---|---|---|
| Acute (immediate) | During transfusion or within 24 hours | Acute hemolytic reaction (ABO incompatibility), febrile non-hemolytic reaction, allergic/anaphylactic reaction, TACO, TRALI, septic reaction |
| Delayed | > 24 hours (days to weeks) | Delayed hemolytic reaction (3-10 days), graft-vs-host disease, post-transfusion purpura |
Key details from authoritative textbooks:
- Acute reactions occur during or within several hours of transfusion; the cutoff used to define "acute" is 24 hours after the end of the transfusion. (Tietz Textbook of Laboratory Medicine, 7th Ed.)
- Scott-Brown's Otorhinolaryngology explicitly states: "These [acute transfusion reactions] present within 24 hours of the transfusion."
- Febrile non-hemolytic reactions specifically occur within 4 hours of stopping the transfusion. (Goldman-Cecil Medicine)
- The most severe reaction - acute hemolytic transfusion reaction (AHTR) due to ABO incompatibility - begins immediately or within minutes of starting the infusion.
For MCQ purposes: The answer is 24 hours - this is the standard cutoff used to distinguish acute from delayed transfusion reactions.
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