SAB
(virtual crossmatch) | Flow crossmatch | CDC crossmatch | Interpretation |
| Positive | Positive | Positive | - Significant burden of DSA
- High risk of hyperacute rejection
|
| Positive | Positive | Negative | - Moderate burden of DSA
- Non-complement-fixing DSA
|
| Positive | Negative | Negative | - Lowest burden of DSA
- Different serum samples used for SAB versus crossmatch testing (historical DSA)
- Identifies an antibody that is specific to an allele that donor does not have
- False-positive SAB test (no "true" DSA) due to:
- High background (serum factors binding to latex beads)
- Binding to denatured antigen
- Low threshold for calling an antibody present (overcalling)
|
| Negative | Positive | Positive | - Non-HLA IgG binding to cell surface antigens found on lymphocytes
- Drug interference (eg, rituximab, ATG, alemtuzumab, IVIG) where binding of the therapeutic antibody to lymphocytes is detected by the assay
- Antibodies against particular loci may not be routinely reported by HLA laboratory
- Different serum samples used for SAB versus crossmatch testing (DSA currently present, development of new DSA from an interval sensitizing event, or burden higher in serum used for crossmatch)
- False-negative SAB:
- Donor antigen/allele is not represented in the bead panel
- For class II: Donor alpha/beta chain combination not represented by bead panel
- Presence of inhibitors in serum ("prozone" effect)
- Presence of IgM/IVIG binding to the beads that masks detection of IgG alloantibody
- Low-level anti-HLA antibody against a shared epitope that is "diluted out" across multiple beads (under-representing true antibody burden)
|
| Negative | Negative | Positive | - IgM antibody (can be either anti-HLA or non-HLA)
|
| Negative | Positive | Negative | - Low-level IgG non-HLA antibody
- False-negative SAB test (refer to above)
|
