Risks and Complications of ABO Incompatible Kidney Transplantation
Despite successful outcomes, ABOi transplantation carries a higher risk of specific complications compared to compatible procedures:
Antibody-Mediated Rejection (ABMR)
ABOi recipients have a significantly higher risk of ABMR, which occurs in roughly 10% of cases compared to 2% in ABOc recipients. This risk is most prevalent in the first week after transplantation.
Infectious Complications
Recipients of ABO-incompatible (ABOi) kidney transplants face a significantly higher risk of infectious complications and infection-related mortality compared to those receiving ABO-compatible (ABOc) transplants.
- Mortality Data: Approximately 49% of deaths in ABOi patients are of infectious origin, compared to only 13% in compatible patients.
- Viral Infections: There is a slightly higher incidence of viral infections:
- BK Viremia: ~14% in ABOi vs. 8% in ABOc.
- CMV (Cytomegalovirus): ~22% in ABOi vs. 19% in ABOc.
- High-Titer Risk: Higher rates of adenovirus and herpes zoster have also been observed. The risk of bacterial infections is significantly higher in patients with high antibody titers (≥1:128), as they require more frequent antibody removal sessions and aggressive immunosuppression.
- Specific Conditions: Includes complicated urinary tract infections (UTIs) and catheter-related infections involving multidrug-resistant bacteria. This is primarily attributed to intensive desensitization and immunosuppressive regimens.
Bleeding Risk
There is a doubled risk of postoperative bleeding in ABOi recipients.
- Primary Cause: This is strongly associated with the number of preoperative immunoadsorption (IA) or plasmapheresis sessions.
- Platelet Function: These sessions can cause a drop in platelet count (averaging a 28% decrease) and potentially lead to platelet dysfunction. Roughly 22% of ABOi recipients begin surgery with a platelet count below 100 x 10⁹/L.
- Clinical Observation: Beyond quantity, contact with plasma filter membranes is hypothesized to induce dysfunction, contributing to the clinical observation that these patients “ooze easily.” This risk remains consistent regardless of the specific filtration technique used.
Quantitative Risk Comparison
- Transfusions: ABOi recipients require red blood cell transfusions more than twice as frequently as compatible controls (29% vs. 12%).
- Predictor: The primary predictor of bleeding is the total number of preoperative antibody-removal sessions. Each additional session independently increases the risk of needing a transfusion.
Factors Influencing Outcomes
- Antibody Titers: Higher baseline and preoperative anti-ABO antibody titers (≥1:128) are associated with an increased risk of rejection, graft failure, and infectious complications. Low-titer recipients (≤1:64) typically show a more significant survival benefit.
- Induction Therapy: The choice of induction agent is critical. Protocols combining T-cell and B-cell targeted therapies (ATG and Rituximab) have shown lower rejection rates and better outcomes than using Rituximab alone.
- Recipient Blood Group: Patients with blood group O often have higher anti-A/B titers, which can be a risk factor for early graft deterioration.
- Accommodation: A key concept in ABOi success is “accommodation,” where the allograft acquires resistance to antibody-mediated injury, allowing it to function normally even in the presence of circulating anti-A/B antibodies.
Conclusion
In summary, while ABOi transplantation requires more intensive desensitization and carries higher immediate risks of rejection and infection, it remains a highly effective strategy to expand the donor pool for patients who would otherwise remain on dialysis.
