*Purpose: Pre-transplant circulating antibodies (Abs) are known to impact outcome after heart transplantation (HTx). Abs can now be detected by single-bead assay but also characterized by 1:8 dilution to detect true high levels. In addition, Abs can be characterized by their ability to bind complement (C1q assay). It has not been firmly established whether patients (pts) awaiting Htx with positive 1:8 dilution Abs and/or C1q+ Abs have worse prognoses after HTx.

*Methods: Between 2010-14, we assessed 423 pts awaiting HTx and divided them into pts with 1:8 dilution positive Abs (n=32) and those without (n=391) and those with C1q+ Abs (n=21) and those without (n=402) at the time of HTx. No DSA were crossed in both study groups at the time of HTx. Both groups were assessed for post-transplant 5-year survival, freedom from cardiac allograft vasculopathy (CAV), freedom from non-fatal major adverse cardiac events (NF-MACE: myocardial infarction, percutaneous coronary intervention new congestive heart failure, pacemaker/defibrillator implant, stroke), and 1-year freedom from rejection (any treated rejection (ATR), acute cellular rejection (ACR), antibody mediated rejection (AMR)).

*Results: Pts with pre-transplant 1:8 dilution positive Abs pre-transplant appear to have decreased freedom from AMR compared to pts without 1:8 dilution positive Abs. There were no significant differences between pts with 1:8 dilution positive and 1:8 dilution negative antibodies in terms of survival, freedom from CAV, or freedom from NF-MACE. When divided into patients with and without C1q+ Abs, there were no differences in all endpoints.

*Conclusions: Pre-transplant 1:8 dilution positive Abs appear to increase risk of AMR after HTx. Larger numbers of pre-transplant C1q+ Ab pts may be needed to demonstrate similar association to AMR.

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