P123 Anti-A titer method comparison

Abstract

Aim To determine an appropriate testing method to evaluate the anti-A titer in blood group B renal transplant waitlist patients to qualify for consideration of blood group A2 (A subgroup) donors. UNOS has established a maximum anti-A titer of 8 to qualify for an A to B kidney. Methods A review of methods in use at transplant centers performing ABO incompatible kidney transplants identified four categories of method variation. The four categories were: • Dithiothreitol (DTT) treatment of serum vs. no DTT treatment • Direct agglutination vs. Indirect agglutination (anti-human globulin enhancement) ∘ Direct = Room Temperature Test Tube or MTS-Gel buffer card ∘ Indirect = Anti-IgG Test Tube or MTS-Gel anti-IgG card • Test Tube method vs. MTS-Gel microcolumn method • A1 target cells vs. A2 target cells Standard commercial blood bank reagents were used for all testing. The same technologist performed all testing. Ten blood group B patients from the kidney transplant waitlist were tested using 8 different methods. After choosing the preferred variable for each of the first three categories, 15 group B potential recipients were tested comparing A1 vs. A2 target cells. Results The categories of Test Tube vs. MTS-Gel and Direct vs. Indirect agglutination had little impact on titers. Pretreatment of serum with DTT provided qualifying titers for three times as many patients as using serum not treated with DTT. DTT pretreatment of serum was chosen along with the indirect agglutination method to optimize detection of IgG anti-A. Using the DTT – Indirect – MTS Gel titer method, comparing A1 vs. A2 target cells with 15 samples showed the choice of target cells also impacted titers. 8 of 15 patients had a 3-fold or greater titer increase using A1 cells compared to A2 cells. 11 of 15 patients (73%) had a qualifying titer with A1cells, compared to 100% with A2 cells. Conclusions Use of DTT treated serum and A2 cells were associated with the lowest anti-A titers. Efforts to establish acceptable method specific titer limits are encouraged.