Positive crossmatches--when is it safe to transplant?

There is no doubt that the interpretation of a positive lymphocytotoxic crossmatch test has changed over the past 10-15 years. It is now generally accepted that the original dogma put forward in the mid-1960s "that a renal transplant must not be performed in the presence of a positive lymphocytotoxic crossmatch" is no longer tenable, and many positive crossmatch transplants have already been successfully carried out. However, the precise conditions under which such a transplant can be performed are still not fully understood. Some factors which should be considered when deciding whether or not to transplant in the presence of a positive crossmatch are: (1) the specificity of the antibody, and this can be HLA class I, class II or non-HLA; (2) the time interval between the last positive crossmatch serum and transplantation; and (3) the immunoglobulin class of the antibody, either IgG or IgM.