(P-IG-35) Our Experience in Using A1 Lectin for Solid Organ Transplant Triaging Between Group A1 and Non-Group A1 Donors

Background/Case Studies: The lectin extracted from the seeds of Dolichos biflorus is known to agglutinate A1 red blood cells (RBC) and is commonly referred to as Anti-A1. This lectin does not contain anti-A1 specifically, but rather Anti-A. Because of the quantitative difference of A antigen binding sites on A1 cells compared to A2 and other Asubgroup cells (roughly 2 million versus 500,000 respectively), Anti-A1 lectin can be diluted to agglutinate only red cells with enough binding sites to produce antibody-mediated lattice formation. ABO molecular testing via real-time PCR targets ABO genes to determine predicted phenotype based on genotype. This case presents a comparison between the two methods to evaluate lectin reliability.

Study

Design/Methods: On 01/02/2020, our Immunohematology Reference Laboratory (IRL) began ABO/Rh testing for a solid organ transplant client requiring A1 lectin testing and reflex ABO molecular testing on all samples which result as blood types A or AB. The client uses initial lectin results to make crucial preliminary decisions in matching solid organ donors with recipients, making timely and accurate results essential. The molecular result serves as confirmation of the serological result. Correlation between A1 lectin and ABO molecular results is important as transplants are being organized based on the initial information provided. Per the Anti-A1 lectin package insert, any agglutination should be interpreted as a positive result and is therefore classified as A1. No agglutination should be interpreted as negative and classified as non-A1.

Results/Findings: Since the implementation of ABO Molecular testing, IRL has observed five cases where the A1 lectin results and the ABO molecular results do not correlate. In all examples, the A1 lectin result was positive, ranging in strength of reactivity from 2+ to 3+. Six samples were genetically A2O and one sample was A2A2. It is also interesting to note that in three of the samples, mixed-field reactivity was observed with Anti-A1 lectin even though the samples were pre-transfusion. Mixed-field reactivity can be indicative of the subgroup A3, but typically will show mixed-field reactivity with Anti-A and no agglutination with Anti-A1. We have not observed any other genetic A subgroups besides A2 to date.

Conclusions: Due to the nature of Anti-A1 lectin manufacturing, it is plausible that an under-diluted reagent could show agglutination when tested against some A2 red cells. Caution should be used in result interpretation when reactivity is less than 4+ positive. Anti-A1 lectin testing should be used only as a tool to determine if cells are A1 positive when strong 4+ reactivity is observed. However, we cannot definitively say that weaker reactivity observed with Anti-A1 lectin indicates an A1 positive cell. Molecular testing is a helpful tool to use in tandem with serological results, as it can be used to confirm indeterminate serological results.

Importance of research: Solid organ transplants have a limited viability window for usage. A quick method of being able to triage between group A1 and non Group A1 donors is important to be most appropriate in allocation of these precious organs in a way that has the highest chance of not being rejected. This abstract discusses using the A1 lectin from Dolichos biflorus as a fast triaging methodology and how it compares to molecular testing via real time PCR.