Overview
Immunohematology principles describe how blood group antigens and corresponding antibodies interact under controlled laboratory conditions so the MLS can detect, grade, and document reactivity that supports typing and compatibility decisions.
Classification
| Phase | Typical condition | Educational purpose |
|---|---|---|
| Immediate spin | Immediate centrifugation / RT read per method | ABO and some cold-reactive patterns |
| 37 °C | Body-temperature incubation when required | Warm-reactive antibody opportunity |
| AHG (IAT) | Wash + anti-human globulin | Detect bound IgG not visible by direct agglutination alone |
Morphologic Features
Not a cell-morphology topic. Visual endpoint is agglutination pattern (or hemolysis) in the test system used.
Laboratory Characteristics
- Method-specific appearance (tube button, gel line, solid-phase signal)
- Required control steps (e.g., check cells after negative AHG)
- Worksheet/LIS capture of grade and phase
- Reagent cell and antiserum lot traceability per SOP
Reference Intervals
Agglutination grades are semi-quantitative observations, not reference intervals. Institutional criteria define when weak reactions require repeat or workup, verify locally; do not invent numeric cutoffs.
Clinical and Laboratory Significance
Correct detection and grading of reactivity underpin ABO/Rh typing, antibody screening, and crossmatch interpretation that protect patients from incompatible transfusion.
Differential Considerations
Distinguish technical positives (dirty glassware, overcentrifugation, fibrin, rouleaux where applicable) from true antigen–antibody reactivity using method troubleshooting and SOP, not guesswork.
Comparison Tables
Agglutination grading (verify institutional guide)
| Grade | Educational appearance | Action mindset |
|---|---|---|
| 0 | No clumps; smooth resuspension | Negative, complete required controls |
| 1+ | Small aggregates; cloudy background | Positive, document; follow weak-reaction SOP |
| 2+ | Medium aggregates | Positive, document phase |
| 3+ | Large aggregates | Strong positive |
| 4+ | Single solid button; clear background | Complete agglutination |
Classification Frameworks
Not applicable.
Laboratory Notes
- Record phase with grade, strength without phase is incomplete
- Do not equate screen reactivity with identified specificity
- Follow local SOP for positive screens before elective RBC issue
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).
- U.S. Food and Drug Administration. Code of Federal Regulations Title 21 . Blood and Blood Components (verify current institutional adoption).
Frequently Asked Questions
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