Overview
The AHG (antihuman globulin) crossmatch is a serologic compatibility test that carries patient plasma/serum combined with donor red cells through an immediate-spin read, a 37°C incubation, and an antiglobulin (AHG) phase, extending detection beyond ABO and cold-reactive antibodies to IgG alloantibodies reactive at 37°C.
Classification
| Phase | Primary detection target |
|---|---|
| Immediate spin | ABO incompatibility; some cold-reactive antibodies |
| 37°C incubation | Sets up antibody sensitization for the AHG phase |
| AHG (antiglobulin) | IgG antibodies, including clinically significant alloantibodies |
Morphologic Features
Not a cell-morphology topic. Relevant findings are agglutination/hemolysis patterns read at each crossmatch phase.
Laboratory Characteristics
- Performed with donor red cells from the unit's attached segment, not a separate stored aliquot
- Incubation time, temperature, and enhancement medium follow the manufacturer insert and institutional SOP
- Adequate washing before AHG addition is required, inadequate washing risks a false negative
- Check cells are added to every AHG-negative tube and must react before the negative is accepted
Reference Intervals
Not a quantitative test, results are qualitative (compatible/incompatible) per phase. Method-specific incubation parameters and enhancement media are manufacturer- and institution-specific; verify against current SOP.
Clinical and Laboratory Significance
A validated compatible AHG crossmatch supports serologic compatibility at the phases tested for that specific donor unit; it is one component of overall pretransfusion compatibility alongside ABO/Rh typing, the antibody screen, and clerical checks.
Differential Considerations
An AHG-phase reaction should be worked up to distinguish true antibody-mediated incompatibility from rouleaux, warm autoantibody interference, or a technical/wash error before a final disposition is assigned to the unit.
Comparison Tables
Crossmatch method comparison
| Method | Detects IgG at 37°C? | Typical indication |
|---|---|---|
| Electronic crossmatch | No | No current or historical clinically significant antibody; two concordant ABO determinations |
| Immediate-spin crossmatch | No | No current or historical clinically significant antibody, when electronic method unavailable |
| AHG crossmatch | Yes | Current or historical clinically significant antibody |
Classification Frameworks
Not applicable, laboratory compatibility test, not a WHO disease classification.
Laboratory Notes
- History of a clinically significant antibody mandates the AHG crossmatch regardless of today's screen result
- Reproducible, unexplained 37°C/AHG reactivity is a hard stop pending workup, do not assume a benign cause
- No valid check-cell reaction, no valid negative result
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).
- Clinical and Laboratory Standards Institute. Related immunohematology and specimen identity standards (verify current documents and institutional adoption).
Frequently Asked Questions
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