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Virtual cross match (vXM)
In a vXM, profiles of HLA antibody reactivity from recently tested recipient samples, plus HLA typing of a deceased donor, are used to predict reactivity in advance of donor cells becoming available. Enables transplant to go ahead with certainty and shorter cold ischaemic times. Only suitable for low-risk recipients with no detectable HLA-donor specific antibodies (DSA) or HLA antibody negative patients on the vXM list.
Prospective cross match
For all other recipients, a full crossmatch must be performed using donor lymphocytes with recipient serum. Recipient serum usually must be fresh; occasionally a recent stored sample may be useful but later confirmation will then usually be required.
Send spleen and lymph nodes to SNBTS H&I staff for an urgent crossmatch. Please ensure that a completed SNBTS histocompatibility / platelet immuno-haematology form is sent with the tissue.
Results will be reported to the renal recipient coordinator. In addition, a direct conversation should be had between consultant surgeon on call and H&I consultant.
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About crossmatching and methods to detect anti-donor antibodies (DSA)
Flow cytometry – fresh donor lymphocytes are mixed with recipient serum and analysed by Flow Cytometry to detect recipient antibody binding to T and B lymphocytes. As well as identifying HLA antibodies the assay may also detect clinically non-relevant non-HLA antibodies. Interpretation of the Flow crossmatch data requires HLA antibody data from a fresh or recent patient sample.
Solid phase assay (e.g. Luminex) – recipient’s serum is tested against a panel of purified HLA molecules to detect the precise targets of any anti-HLA antibodies. This assay is conducted without knowledge of potential donors, in advance of transplantation, or for monitoring post-transplant. Having uniformly low titres of DSA to donor antigens without a history of previous exposure to foreign HLA antigens makes a positive crossmatch very unlikely – this is the basis of the Virtual Crossmatch (vXM).