Overview
Acute hemolytic transfusion reaction (AHTR) is hemolysis occurring during or within roughly 24 hours of transfusion. The most severe form is ABO-incompatible AHTR: pre-formed, complement-fixing IgM anti-A/anti-B react with incompatible donor red cell antigens, causing immediate intravascular hemolysis, almost always traceable to a clerical or identification error rather than a testing failure.
Classification
| Category | Typical mechanism | Laboratory hallmark |
|---|---|---|
| ABO-incompatible AHTR | Complement-fixing IgM anti-A/anti-B, intravascular hemolysis | Clerical error + hemoglobinemia + positive DAT + ABO mismatch |
| Non-ABO antibody-mediated acute hemolysis | IgG alloantibody, often extravascular | Positive DAT without ABO discrepancy; may require antibody workup |
| Non-hemolytic reaction (for comparison) | Not antibody-mediated hemolysis | Clean clerical check, unremarkable plasma, negative DAT, concordant ABO typing |
Morphologic Features
Not a cell-morphology topic, this is a reaction-investigation and interpretation reference.
Laboratory Characteristics
- Clerical check compares patient ID band/barcode, unit tag, requisition, and computer record
- Visual inspection compares post-reaction plasma/serum against the pretransfusion specimen for hemoglobinemia
- DAT on the post-reaction specimen may show a positive or mixed-field pattern
- Repeat ABO/Rh typing on the post-reaction specimen plus a direct recheck of the implicated unit's segment/label
Reference Intervals
Not applicable in the quantitative sense, this is a qualitative investigation pathway. Institutional turnaround-time targets and extended-workup triggers (haptoglobin, bilirubin, plasma-free hemoglobin) are SOP-specific; verify against current institutional protocol.
Clinical and Laboratory Significance
The combined pattern of clerical discrepancy, hemoglobinemia, positive DAT, and ABO mismatch is what distinguishes a true ABO-incompatible AHTR from other reaction categories. A clerical discrepancy found in isolation is treated as an immediate-notification finding on its own, independent of what the hemolysis markers eventually show.
Differential Considerations
Distinguish ABO-incompatible AHTR from non-ABO antibody-mediated acute hemolysis (positive DAT without an ABO discrepancy), from delayed hemolytic/serologic reactions (anamnestic response, days later), and from non-hemolytic categories such as febrile non-hemolytic or allergic reactions (clean hemolysis workup).
Comparison Tables
Reading the AHTR workup panel
| Finding | Supports ABO-incompatible AHTR | Argues against it |
|---|---|---|
| Clerical check | Discrepancy found (wrong unit/patient) | Clean match across all identifiers |
| Post-reaction plasma | Visible pink/red hemoglobinemia | Visually unremarkable, similar to pretransfusion sample |
| DAT | Positive, often mixed-field | Negative |
| ABO/Rh recheck | Mismatch between unit and patient | Concordant with pretransfusion type and issued unit |
Classification Frameworks
Not applicable, laboratory reaction-investigation pathway, not a WHO disease classification.
Laboratory Notes
- Clerical check first, it is the fastest step and the most common root cause of true ABO-incompatible AHTR
- A clerical discrepancy alone is an immediate-notification, unit-quarantine finding, regardless of hemolysis markers
- A negative DAT does not exclude an evolving or already-cleared hemolytic process, interpret it with the full panel and clinical trajectory
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Cohn CS, Delaney M, Johnson ST, Katz LM, eds. Technical Manual. 21st ed. AABB; 2023.
- Harmening DM. Modern Blood Banking & Transfusion Practices. 7th ed. F.A. Davis; 2019.
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- AABB. Standards for Blood Banks and Transfusion Services (verify current edition and institutional adoption).
- World Health Organization. Blood safety and availability / transfusion guidance (verify current WHO publication and institutional adoption).
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