Department of Pathology, Division Transfusion Medicine, Johns Hopkins All Children’s Hospital, St. Petersburg, Florida. St. Petersburg, Florida, United States
Background/Case Studies: Performing a reverse type on neonates less than 4 months old has been deemed unnecessary as the patient’s back-type is not fully developed due to immunologic immaturity. However, over the past 20 years, especially in those patients less than 4 months, ABO incompatible heart transplant has become possible with outcomes rivaling ABO compatible transplants. Type O neonates requiring heart transplant have the longest wait on the transplant list and the move to ABO incompatible heart transplantation has been lifesaving for those infants. Prevention of hyperacute rejection is a major concern in ABO incompatible heart transplant and anti-A and anti-B isohemagglutinin titer levels, whether passively acquired from maternal source or naturally occurring, play a vital role in ABO incompatible heart transplant eligibility. The hypothesis of this investigation is that group O neonates less than 4 months old will demonstrate variable titers of ABO antibodies.
Study
Design/Methods: Randomly selected group O neonates were tested for the presence of ABO antibodies per the “Isohemagglutinin Titer (Titer A and Titer B)” standard operating procedure at a free-standing children’s hospital using retained blood bank samples. Once antibody presence was established, an isohemagglutinin titer was performed. Samples were tested for isohemagglutinins, anti-A and -B and titered (IgM and IgG). ABO reverse typing and isohemagglutinin titers were performed using standard tube method. Anti-A and -B were tested by gel indirect antiglobulin test (IAT).
Results/Findings: Group O neonates (N=25), mean age 14.5 days (range 2 hrs-12 weeks) were tested. Ninety-two percent of non-specific isohemagglutinins were detected by either immediate spin tube technique (72%) or demonstrated after 30 minutes at 4°C (48%) Patients who had ample serum remaining were titered for anti-A and anti-B. Anti-A titers (N=8) were found to have a range of 1:2-1:128 and anti-B (N=8) titers range was 1:4-1:32. Conclusions: This study demonstrates ABO isohemagglutinin presence and titer strength is variable in many group O neonates. This underappreciated finding may have significant implications for those group O neonates requiring ABO incompatible heart transplant as the critical value for eligibility is a titer of 1:16. More studies of neonatal reverse typing are needed and thus the algorithm applied here may be useful to study or adopt in other facilities that perform ABO incompatible heart transplants.
Importance of research: ABO compatibility is a major barrier for heart transplantation, particularly in neonatal populations in which there is a scarcity of supply. The naivety of their immune system is favorable for survivability and positive outcomes. Data regarding neonatal isohemagglutinin titers is currently limited due to lack of testing. Establishing data in other facilities that participate in ABO incompatible heart transplants can facilitate in the wait time and transfusion protocols for these patients.
