Aim: The new Kidney Allocation System has increased requests for virtual crossmatches (VXM) to predict the possibility of a negative donor specific crossmatch. This study evaluates the efficacy of an in-house generated algorithm to predict and quantify the allogeneic crossmatch.

Method: A retrospective review was conducted on 50 flow cytometric crossmatch (FXM) results that were collected from the database reflecting several different median channel shift values. The corresponding HLA Class I and Class II antibody screening was performed using Flow-PRA screen beads (One Lambda). Luminex Class I and Class II single antigen bead (SAB) testing and analysis for mean fluorescent intensity was also performed. A calibration curve for predicting the VXM was developed by comparing the mean fluorescent intensity values for the donor specific antibodies obtained from the Luminex SAB results to the corresponding median channel shift values from the FXM results. A regression analysis was performed on the median channel shift versus mean fluorescent intensity values and the slope was calculated.

Results: We reviewed 246 FXM results that were positive for T-cell and/or B-cell performed between August 2008 and February 2013. We substituted the highest mean fluorescent intensity values from the database for either the HLA Class I or Class II specificities in the VXM algorithm. We observed that our in-house generated VXM algorithm had an overall positive predictive value of 91% for the T-cell and B-cell crossmatches. Our VXM algorithm is unique as it is the only VXM algorithm that calculates a range of median channel shift values for the FXM, thus increasing the predictability of the actual FXM. There were about 9% of crossmatches that were predicted as negative using our VXM algorithm that were positive by FXM evaluation. This could be due to prozone-like phenomenon, antibodies dependent on the conformational characteristics of the antigen, antibody avidity & affinity, or allele specificities not on the Luminex SAB panel. After implementation of the new Kidney Allocation System, we observed a 25% increase in the requests for VXM which resulted in a 15% decrease in the discard rate of kidneys.

Conclusion: The VXM algorithm shows a high probability of accurately predicting FXM results and may mimic the sensitivity of the final crossmatch, thus reducing the time and cost for deceased donor work-up. This could allow for quicker organ allocation for sensitized patients.

CITATION INFORMATION: Rao P, Deo D, Rhodes C, King D, Bowe P, Napoleon J, Okere I. A Virtual Crossmatch Algorithm That Mimics the Sensitivity of Flow Cytometric Crossmatch. Am J Transplant. 2016;16 (suppl 3).

« Back to 2016 American Transplant Congress