Crossmatch Testing

Flow Cytometer Crossmatch (FCXM)

Tests

• T & B-Cell XM by Flow Cytometry
• T & B-Cell XM-Pronase Treatment

Purpose

• To detect donor-specific antibodies pre- or post-transplant (donor cells as targets).
• To detect autoantibodies (recipient cells as targets).

Highlights  

• The laboratory performs three-color flow cytometer crossmatch (FCXM) that detects the presence or absence of IgG antibodies directed towards donor lymphocyte-specific antigens.
• Donor lymphocytes are isolated from whole blood, lymph nodes and spleen using various methods that will yield highly purified lymphocytes (free from platelets, monocytes, and neutrophils) for optimal sensitivity and therefore more accurate crossmatch test results.
• The laboratory treats lymphocytes with Pronase to reduce background reactivity in a B cell FCXM due to non-specific immunoglobulin binding by Fc receptors and B-cell surface immunoglobulins. The laboratory performs parallel crossmatch on both untreated and Pronase-treated cells.
• ITL reports crossmatch test results as Negative or Positive. The report also displays the strength of the crossmatch in median channel shift (MCS), the strength of donor-specific HLA antibodies if any (in MFI), and a comment indicating the risk of accelerated rejection.
• The use of 96-well plate format enables the laboratory to perform 8 donor-recipient pairs FCXM per plate/run. With two FACS canto flow cytometers, the laboratory can perform 16 donor-recipient pairs FCXM per run.

• Routine testing reported in ≤ 3 business days.
• STAT testing reported in 1 business day.
• Physical crossmatch required prior to transplant is reported within 5 hours of request.  

Virtual Crossmatch (VXM) 

Test

• Virtual Crossmatch 

Purpose

• To determine the presence of pre-transplant donor-specific HLA antibodies without physical crossmatch and assess the risk of accelerated rejection. A virtual crossmatch based strategy facilitates sharing of deceased donor kidneys for highly sensitized recipients. 

Highlights

• Virtual crossmatch is a crossmatch that determines the compatibility of a donor and recipient pair without performing a physical crossmatch (i.e., flow cytometric crossmatch). 
• Virtual crossmatch involves a determination of the presence or absence of donor-specific HLA antibodies (DSA) in a patient by comparing the patient’s HLA antibody specificity profile to the HLA types of the proposed donor. 
• ITL performs VXM based on data that is collected continuously since 2013 to determine the relationships between the strengths of flow cytometric crossmatch (in Median Channel Shift - MCS) and DSA (Mean Florescent Intensity - MFI).
• ITL VXM protocol is reliable, has shown to have an excellent kidney graft survival, and works even for recipients with 100% cPRA, Roll and Rajalingam et al. Transplantation, 2019.
• Over 90% of solid organ transplantations (kidney, heart, and lung) performed at the UCSF transplant programs (approximately 500 transplants per year) are based on VXM as final crossmatch. 
• VXM report is comprehensive and displays, 1) the predicted physical crossmatch results as either negative or positive, 2) donor-specific HLA antibodies if any and their strength in MFI, 3) risk assessment comments, 4) the HLA typing of patient and donor in serological equivalents, and 5) HLA antibody specificities detected in the most recent serum sample with their corresponding MFI values. VXM report is available to the transplant team prior to surgery. 

• Reported in 10-30 minutes. 

Endothelial Cell Crossmatch to Detect Non-HLA Antibodies (EXM)

Test

• Endothelial cell crossmatch 

Purpose

• To detect non-HLA antibodies that have been implicated in antibody-mediated rejections.  

Highlights  

• Uses two to four endothelial cell (EC) lines selected based on patient’s HLA antibody profile to avoid any HLA antibody-mediated positivity.
• EC crossmatch is performed using flow cytometry.
• EC crossmatch report shows test results as Negative or Positive. The report also displays the strength of the crossmatch in median channel shift (MCS), and a comment indicating the risk of accelerated rejection if any.
• Positive EC crossmatch may indicate the presence of antibodies directed to non-HLA targets expressed on endothelial cells, which have been implicated in antibody-mediated rejection. 

• Routine testing reported in 3 business days.
• STAT testing reported in 1 business day.