The cross-match test is an in vitro test to determine the presence of anti-lymphocyte antibody to donor cell antigens (lymphocytotoxic antibody) in serum of an individual with preformed antibodies to donor cells. Examples are recipients for an organ transplant or a couple with a history of recurrent spontaneous abortions. The recipient serum is incubated with donor lymphocytes and the binding can be detected by flow cytometry analysis (with fluorescent conjugated reagent). If cytotoxic antibodies are present in maternal serum, they will combine with the surface antigens of donor lymphocytes; the amount of fluorescence on the cells (percentage of positive T or B cells), as measured by flow cytometry, is proportional to the amount of antibody (flow cytometry cross-match).