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Crossmatch (CDC, flow, virtual)

The crossmatch detects recipient antibodies against donor antigens, by complement-dependent cytotoxicity, flow cytometry, or as a virtual crossmatch.

Reviewed by Independent editorial compilation on June 23, 2026Educational reference, not medical advice

A crossmatch is a pre-transplant immunologic test that determines whether a prospective recipient carries antibodies directed against a specific donor's cells or human leukocyte antigens (HLA).[1][2] A positive crossmatch indicates the presence of donor-reactive antibody and, in the classic case, predicts hyperacute rejection of the graft; historically a positive complement-dependent crossmatch was an absolute contraindication to transplantation.[1][3] Three principal approaches are in clinical use: the complement-dependent cytotoxicity (CDC) crossmatch, the flow-cytometric crossmatch, and the virtual crossmatch.[2][4] The crossmatch is the final immunologic check before solid-organ transplantation and is interpreted together with HLA typing and the recipient's antibody profile (see Human leukocyte antigen (HLA) and tissue typing and Donor-specific antibodies (DSA)).[2]

Purpose and principle

The fundamental question a crossmatch answers is whether the recipient's serum will react with the donor's antigens.[1][2] Because preformed antibodies against donor HLA (or, less commonly, against donor ABO or other antigens) can bind donor endothelium and trigger complement activation and thrombosis within minutes to hours of reperfusion, detecting them beforehand prevents catastrophic early graft loss.[1][3] The historical observation by Patel and Terasaki in 1969, that recipients with a positive lymphocyte crossmatch suffered immediate graft failure, established the crossmatch as the gatekeeper of solid-organ transplantation.[3]

Complement-dependent cytotoxicity (CDC) crossmatch

In the CDC crossmatch, donor lymphocytes (separated into T-cell and B-cell fractions) are incubated with recipient serum; rabbit complement is then added.[1][2] If the recipient's serum contains antibody that binds the donor cells and fixes complement, the donor cells are lysed; cell death is read out with a vital dye and scored. Cell killing constitutes a positive crossmatch.[1][2]

The CDC method detects only complement-fixing antibodies and requires antibody above a threshold density, so it is relatively specific for clinically dangerous antibody but less sensitive than newer methods.[2][4] Its sensitivity can be increased by adding an anti-human globulin (AHG) augmentation step. Because the assay can be confounded by non-HLA (for example, autoreactive) IgM antibodies, a dithiothreitol (DTT) treatment step is often used to distinguish clinically relevant IgG from IgM.[2] A positive T-cell CDC crossmatch (reflecting class I HLA antibody) is generally a contraindication to transplantation; the interpretation of an isolated positive B-cell crossmatch is more nuanced.[2][4]

Flow-cytometric crossmatch

The flow-cytometric crossmatch (FCXM) incubates donor lymphocytes with recipient serum and detects bound recipient antibody using a fluorochrome-labeled anti-human IgG, with T cells and B cells distinguished by lineage markers.[2][4] Antibody binding shifts the fluorescence channel relative to a negative control, reported as a channel shift.[4]

The FCXM is considerably more sensitive than the CDC method and detects antibody whether or not it fixes complement, allowing it to identify lower-level donor-reactive antibody.[2][4] This sensitivity is valuable for risk stratification in sensitized candidates but comes at the cost of lower specificity, since it can detect antibody at levels of uncertain clinical significance. A positive FCXM with a negative CDC crossmatch denotes an intermediate immunologic risk that is weighed against the candidate's antibody specificities and the planned immunosuppression.[2][4]

Virtual crossmatch

The virtual crossmatch (VXM) is not a wet-laboratory test on donor cells but a comparison, performed in silico, of the recipient's defined HLA-antibody specificities (identified by single-antigen bead solid-phase assay) against the donor's HLA type.[2][5] If the donor expresses an HLA antigen to which the recipient has antibody (an "unacceptable antigen"), the virtual crossmatch is predicted positive; if not, it is predicted negative.[5]

The virtual crossmatch depends on two prerequisites: an accurately characterized recipient antibody profile and a complete donor HLA type.[5] Its principal advantages are speed and reach. Because it requires no shipment of donor cells and no incubation time, it allows transplant centers to assess compatibility with a distant donor in minutes, reducing cold-ischemia time, avoiding futile organ shipments, and expanding access for broadly sensitized candidates.[5][6] In U.S. practice the virtual crossmatch underlies the unacceptable-antigen mechanism in deceased-donor kidney allocation and the calculated panel-reactive antibody (cPRA), and many centers now proceed to transplant on the basis of a negative virtual crossmatch with a physical crossmatch performed retrospectively or omitted for low-risk candidates.[5][6] See Panel-reactive antibody / cPRA and sensitization.

Comparison and interpretation

| Method | Detects | Sensitivity | Requires donor cells | Turnaround | |---|---|---|---|---| | CDC crossmatch | Complement-fixing antibody | Lower | Yes | Hours | | Flow crossmatch | IgG binding (complement-independent) | Higher | Yes | Hours | | Virtual crossmatch | Defined antibody vs donor HLA type | Depends on antibody assignment | No (in silico) | Minutes |

No single assay is definitive in isolation. Results are integrated: the CDC crossmatch reflects the most dangerous, complement-fixing antibody; the flow crossmatch adds sensitivity; and the virtual crossmatch provides specificity-level resolution and logistical speed.[2][4][5] Discordances, for example, a positive flow crossmatch with a negative virtual crossmatch, prompt review for non-HLA antibody, technical artifact, or autoantibody.[2][4] Crossmatch interpretation is a histocompatibility-laboratory and transplant-team judgment and is organ- and program-specific.

See also

  • Human leukocyte antigen (HLA) and tissue typing
  • Panel-reactive antibody / cPRA and sensitization
  • Donor-specific antibodies (DSA)
  • Transplant rejection
  • ABO compatibility and ABO-incompatible transplantation

References

  • Acute Transplantation Rejection. StatPearls. NBK535410. https://www.ncbi.nlm.nih.gov/books/NBK535410/
  • Justiz Vargas AN, et al. Transplantation Immunology. StatPearls. NBK538218. https://www.ncbi.nlm.nih.gov/books/NBK538218/
  • Patel R, Terasaki PI. Significance of the positive crossmatch test in kidney transplantation. N Engl J Med. 1969;280(14):735-739. PMID:4886455.
  • Mulley WR, Kanellis J. Understanding crossmatch testing in organ transplantation: A case-based guide for the general nephrologist. Nephrology (Carlton). 2011;16(2):125-133. PMID:21272123. https://pubmed.ncbi.nlm.nih.gov/21272123/
  • Tambur AR, et al. Sensitization in Transplantation: Assessment of Risk (STAR), virtual crossmatch and antibody assessment. Am J Transplant. 2018;18(7):1604-1614. PMID:29603851. https://pubmed.ncbi.nlm.nih.gov/29603851/
  • Cecka JM, et al. Calculated PRA: initial results show benefits for sensitized patients and a reduction in positive crossmatches. Am J Transplant. 2011;11(4):719-724. PMID:21443677. https://pubmed.ncbi.nlm.nih.gov/21443677/

This article is an educational reference for the donation and transplant workforce and the public. It is not medical advice, and it does not replace institutional policy, OPTN policy, or clinical judgment.

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