Background. Despite the positive impact of flow crossmatching(FCXM) upon alloantibody detection, its inability to distinguish anti-Class I from Class II or non-HLA from HLA-antibodies remain serious limitations which may cause false positive crossmatches. A newly released bead-based commercial assay(Flow DSA-XM) may alleviate these problems and correlate better with DSA identification. The correlation between DSA-XM and conventional FCXM with DSA presence and strength (MFI) was determined.

Methods. First, positive/negative control ranges were established for DSA-XM(OneLambda) using sera from 5 male, 0% PRA patients tested against 5 PBL donors. FCXM ranges already existed in lab. DSA-XM and FCXM were then performed on serum from 40 waitlisted renal patients against 20 donors. DSA were determined by luminex (Immucor, OneLambda).

Results. Separation between mean positive and negative controls for DSA-XM Class I (666-86) were comparable to T-FCXM. In contrast, separation between controls for DSA-XM DQ (198-110) and DSA-XM DR (214-143) were narrow compared to B-FCXM. XM results were then correlated with DSA using sensitivity/specificity analysis. Class I sensitivity/specificity was equivalent between DSA-XM Class I and T-FCXM.

In contrast, sensitivities for DSA-XM DQ and DR were low compared to B-FCXM. Specifity for DSA-XM DR, but not DQ, was better than B-FCXM. Lastly, we correlated DSA strength (MFI) with crossmatch strenth (MCS) by linear regression. T-FCXM MCS showed better correlation with DSA MFI (r²=0.8 vs. r²=0.5) as did B-FCXM vs. DSA-XM DQ(r²=0.6 vs. r²=0.3) or DSA-XM DR(r²=0.1). Results were equivalent with DSA determined using Immucor or OneLambda assays.

Summary. Flow DSA-XM is a novel approach that attempts to discriminate antibody directed against Class I vs. DQ and DR. However, the poor separation between Class II controls complicates determination of meaningful channel shifts. In addition, DSA-XM DQ and DR assays fail to identify lower strength MFI which may cause false negative crossmatches. Neither Class I or II components of DSA-XM correlate well with DSA strength. These issues plus the high cost and short shelf-life of the kit do not show improvements over conventional FCXM but merely create additional problems.

CITATION INFORMATION: Kimball P., McDougan F. Flow DSA-XM: Better Crossmatch or Just Different Problems? Am J Transplant. 2017;17 (suppl 3).

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