Table 1. Risk Stratification of Antibody Mediated Rejection based on the Combination of Single Antigen Beads and Flow Cytometric Crossmatch.

Risk for AMR	Considerations	SAB results	Flow XM results	Further evaluation
Low	No DSA present	Negative	Negative T/B Cell	None
	Alloantibody towards denatured HLA	Positive	Negative T/B Cell	Acid Treatment of SAB. If still positive – the alloantibody is towards denatured HLA
	Laboratory factors	Positive	Negative T/B Cell	Consult with HLA laboratory
	Recent anti-CD 20 treatment	Negative	Positive T and/or B-cell	Pronase treatment of donor lymphocytes
	Auto-antibodies	Negative	Positive T and/or B–cell	Flow auto-crossmatch
High	DSA present	Positive	Positive B-cell	Consider testing for further risk stratification*
	Prozone effect	Weakly positive	Strongly Positive B-cell	Repeat SAB with 1:8 serum dilution to identify possible prozone
	Incomplete donor/recipient HLA typing	Negative	Positive B-Cell	Be sure that the donor and recipient have been typed for DQ alpha and DP
	SAB does not include donor HLA antigen	Negative	Positive B-Cell	If SAB does not include donor antigen, use supplemental SAB kit or another SAB vendor
	Alloantibody to shared epitope	Weakly positive	Positive B-Cell	Review SAB epitope binding patterns with HLA expert
Uncertain	Low HLA expression on donor cells (ex. Cw)	Positive	Negative B-Cell	Consult with HLA laboratory
	DSA with low affinity/avidity	Positive	Negative B-cell	None
	Non-HLA antibody	Weakly positive or negative	Positive T and/or B-cell	Consider checking for non-HLA antibody

The risk of AMR depends on several factors, but mostly depends on SAB and XM testing in clinical context. Ancillary testing including acid treatment of SAB, auto-flow XM, and serum dilution among others can provide additional information for risk stratification. Key: AMR: antibody mediated rejection, SAB: single antigen beads, DSA: donor specific antibody, Flow XM: Flow cytometric crossmatch, HLA: Human leukocyte antigen.

^*Further risk stratification includes DSA quantification, C1q binding ability, and IgG subclass identification if indicated.