Virtual Crossmatch: Reality of Perception

Impact of COVID-19 pandemic on transplant laboratories: How to mitigate?

A positive flow cytometry crossmatch (FCXM) due to donor specific antibodies (DSA) constitutes a risk for kidney transplantation; such a finding may indicates an unacceptable donor for this patient. However, positive FCXM in the absence of DSA is considered discordant and need further investigations. During COVID-19 pandemic, we observed 22% discordant results out of 445 FCXM performed during eight months period in our laboratory and another 7% were invalid due to high background negative control (NC). No study has addressed the impact of COVID-19 pandemic on FCXM and the overall pre-kidney transplant workups or described a solution to deal with these non-specific reactivities. Herein, we analyzed all FCXM results in SARS-CoV-2 seropositive patients and addressed how this pandemic affected significantly the pre-kidney transplant workups, highlighting both technical and financial implications. We also shared our modified FCXM procedures using dithiotheritol (DTT) sera treatment or blocking donor cells with negative control human serum (NCS) which we found to be successful to abrogate 98% of all discordant FCXM results and to validate all invalid results due to high background NC. In conclusion, COVID-19 pandemic has affected our HLA laboratory significantly by creating many false positive or invalid crossmatch results. Transplant laboratories must consider this before test interpretations and immune risk assessments. We recommend the use of DTT serum treatment to remove nonspecific bindings in the sera of kidney transplant candidates and the use of NCS-blocked donor cells to correct high background when performing FCXM in transplant candidates or donors with recent history of SARS-CoV-2 immunization respectively.

BSHI/BTS guidance on crossmatching before deceased donor kidney transplantation

All UK H&I laboratories and transplant units operate under a single national kidney offering policy, but there have been variations in approach regarding when to undertake the pre‐transplant crossmatch test. In order to minimize cold ischaemia times for deceased donor kidney transplantation we sought to find ways to be able to report a crossmatch result as early as possible in the donation process. A panel of experts in transplant surgery, nephrology, specialist nursing in organ donation and H&I (all relevant UK laboratories represented) assessed evidence and opinion concerning five factors that relate to the effectiveness of the crossmatch process, as follows: when the result should be ready for reporting; what level of donor HLA typing is needed; crossmatch sample type and availability; fairness and equity; risks and patient safety. Guidelines aimed at improving practice based on these issues are presented, and we expect that following these will allow H&I laboratories to contribute to reducing CIT in deceased donor kidney transplantation.

The causes and frequency of kidney allograft failure in a low-resource setting: observational data from Iraqi Kurdistan

Background

In the developing world, transplantation is the most common long-term treatment for patients with end-stage renal disease, but rates and causes of graft failure are uncertain.

Methods

This was a retrospective outcomes study of renal transplant patients seen in Iraqi Kurdistan nephrology clinics in the year 2019. In 2019, 871 renal transplant patients were registered and outcomes followed through 12/31/2020. Indicated renal biopsies were obtained on 431 patients at 1 day to 18 years post-transplantation. Outcomes were compared with United States Renal Data System (USRDS) living donor reports.

Results

All donors were living. The recipient age was 38.5 ± 13.3 years, 98.2% were < 65 years old, 3.7% had previous transplants, and 2.8% had pretransplant donor-specific antibodies (DSA). Gehan-Breslow estimated failure rates for all-cause, return to HD, and death with functional graft were 6.0, 4.2, and 1.9% at 1 year and 18.1, 13.7, and 5.1% at 5 years post-engraftment (USRDS 2000; 1 year: 7.0, 5.0, 2.6%; 5 year: 22.3, 15.2, 10.6%. USRDS 2010; 1 year: 3.7, 2.4, 1.4%; 5 year: 15.3, 9.6, 7.3%). The median graft survival was 15 years. Acute tubular injury (ATI), infarction, and acute T cell-mediated rejection accounted for 22.2% of graft loss, with > 75% of these failures taking place in the first year. Most graft failures occurred late, at a median post-transplant time of 1125 (interquartile range, 365–2555) days, and consisted of interstitial fibrosis and tubular atrophy (IF/TA) (23.8%), transplant glomerulopathy (13.7%), and acquired active antibody-mediated rejection (12.0%). The significant predictors of graft loss were C4d + biopsies (P < 0.01) and advanced IF/TA (P < 0.001).

Conclusions

Kurdistan transplant patients had graft failure rates similar to living donors reported by the USRDS for the year 2000 but higher than reported for 2010. Compared to USRDS 2010, Kurdistan patients had a moderate excess of HD failures at one and 5 years post-engraftment. Nevertheless, prolonged survival is the norm, with chronic disorders and acquired DSA being the leading causes of graft loss.

Assessment of Rapid Optimized 96-well Tray Flow Cytometric Crossmatch (Halifax-FCXM) with Luminex Single Antigen Test

INTRODUCTION

Flow cytometric crossmatch assay (FCXM) is a sensitive cell-based method for evaluating the presence of donor-specific antibodies (DSA) before transplantation. Recently, 96-well tray FCXM protocol (Halifax FCXM) with improved test efficiency has been introduced. The objective of the present study was to assess the performance of Halifax FCXM by correlating with DSA results based on single antigen bead (SAB) assays (virtual crossmatch, VXM).

METHODS

A total of 341 FCXMs were evaluated for the detection of HLA-DSA. A positive VXM was defined as having at least one HLA - DSA (HLA-A, B, Cw, DR, DQB1) with ≥ 1000 MFI (mean fluorescence intensity) identified by SAB assay.

RESULTS

Of a total 341 cases, 113 showed class I VXM (+) with class I DSA MFI ≥ 1000 exclusively against one or more donor HLA class I antigens (HLA-A, B, Cw), 72 had class I-/II + DSA, and 156 had VXM(-). Halifax T-FCXM showed a sensitivity of 87.6% (99/113) and a specificity of 98.2% (224/228) for detecting class I VXM (+). The concordance between T-FCXM and class I VXM was 94.7% (323/341). Halifax B-FCXM showed a sensitivity of 58.3% (42/72) and a specificity of 98.7% (154/156) for detecting class I-/II + DSAs. The concordance between B-FCXM and class I-/II + VXM was 86.0% (196/228). When we separately analyzed data, B-FCXM detected HLA-DR (+) (68.8%) and HLA-DQ (+) DSAs (71.0%) similarly (P > 0.05). T-FCXM detected 87.6%, 97.2%, and 98.2% of class I DSA-positive cases with MFI values (sumDSA) ≥ 1000, ≥ 3000, and ≥ 5000, respectively. B-FCXM detected 58.3% of class I-II + DSA -positive (≥1000) cases, but detected 76.7% (33/43) and 89.2% (33/37) of class I-II + DSAs if MFI values of sumDSA and immunodominant DSA (iDSA) were above 5000, respectively. Halifax FCXM had sensitivities of 91.5% and 96.2% for detecting VXM (+) having MFI values above 5000 for class I or class II sumDSA and iDSA, respectively.

CONCLUSION

Halifax FCXM showed a good correlation, especially with SAB assay-based high MFI DSA or sumDSA. Concurrent application of FCXM with VXM can improve pre-transplant risk assessment and progress organ allocation efficiency.

The Impact of Virtual Crossmatch on Cold Ischemic Times and Outcomes Following Kidney Transplantation

BACKGROUND

Prolonged cold ischemic time (CIT) in deceased donor kidney transplantation (DDKT) has been associated with adverse graft outcomes. Virtual crossmatch (VXM) facilitates reliable prediction of crossmatch results based on the profile of human leukocyte antigen antibodies of the recipient and the donor in reduced time compared with a physical crossmatch (PXM). We hypothesized a shorter CIT since the implementation of the VXM in recipients of DDKT.

METHODS

We conducted a retrospective cohort study of consecutive adult recipients of DDKT. The data were analyzed for differences in CIT before and after the implementation of VXM.

RESULTS

After the exclusion of 59 recipients (age less than 18 years and/or CIT ≥ 20 hours), our study compared outcomes of 81 PXMs from February to June 2018 against 68 VXMs from February to June 2019. There were no statistical differences between groups based on donor age (P = .09), donor type (P = .38), kidney donor profile index (P = .43), or delayed graft function (P = .20). Recipients with VXM were older (58 vs 51 years, P = .002) and had a higher estimated post-transplant survival score (59% vs 46%, P = .01). The CIT was significantly lower for the VXM group (P = .04).

CONCLUSION

Our study demonstrated a significantly shorter CIT with VXM in DDKT recipients. Our study was limited with small sample size, but the trend of increased graft survival with higher estimated post-transplant scores and older recipients is encouraging as the donor pool expands with marginal kidneys and national sharing.