Every transplant team wants a definitive answer for the compatibility of a potential recipient with a specific donor. The Mean Equivalent Standard Fluorescence is a level of fluorescence (MESF) that a flow cytometer measures based on the amount of bound IgG antibody on the donor cell. The cutoff MESF determination (positive = black/ negative=white) is developed for each lab based on their program’s priorities. The reality is there are many shades of grey using one predetermined cut off for T and B cells. Our program uses 1500 MESF for T cells and 2500 MESF for B cells. The question is; would a crossmatch resulting in 2100 for T cells and 3100 for B cells be contraindicative of compatibility? We have studied 131 crossmatches from sensitized potential renal transplant recipients and deceased donors. We use a current and historic (<six months) patient sera for T and B cell flow crossmatches. There were 22 positive crossmatches studied out of 131 performed from 7-1-2011 to 6-30-2012. All of the potential renal transplant recipients demonstrated anti-HLA antibodies (N=131). None had demonstrable anti-HLA antibodies to the donor antigens at the time of crossmatch. We use pronase treated cells in a T and B cell flow crossmatch procedure with Mean Equivalent Standard Fluorescence (MESF) as a read out. Several crossmatches (n=13), (59 %) had IgM interference that was reduced with Dithithreatol (DTT). The untreated sera were positive without DTT treatment and became negative after DTT treatment for both T and B cells. Flu vaccination has been shown to increase anti-HLA antibody activity and may result in a B cell non-specific activation or reactivation. In conclusion: The reduction of IgM in potential recipient sera with DTT, in our laboratory, has allowed a greater number of sensitized patients to be transplanted. 2) An auto crossmatch (donor cells and donor sera) is employed to determine background fluorescence i.e. autoantibody status, and 3) black= positive or white= negative in some deceased donor crossmatches is difficult to determine. Each case’s crossmatch result close or ∼500 MESF above the cutoff (grey area) must be evaluated with the patient necessity for that transplant in mind to determine, if the transplant should be performed.

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