Quantitation of residual D positive red cells in D negative recipients of D positive solid organ transplants

Solid organ transplants (SOT) from D positive donors are potentially sensitising events for D negative recipients. For this reason, it is important to quantify the presence of residual D positive red blood cells (RBCs) in the recipient's circulation and calculate the correct dose of prophylactic anti-D (PAD) required to prevent sensitisation. This is especially important in females of child-bearing potential where the presence of allo anti-D can, at worst, cause the death of the fetus in future pregnancies.

This study aimed to identify the patient characteristics of D positive SOT cases referred to Red Cell Immunohaematology, NHSBT for flow cytometry investigation. This information could indicate improvements required in the current testing methodology, as well as to the calculations used to prescribe PAD for this patient group.

Samples were investigated using a Beckman Coulter Navios Flow Cytometer using BRAD3-FITC (anti-D), AEVZ5.3-FITC (isotype matched negative control) and BIRMA17C-PE (granulocyte exclusion reagent). Mollison's calculation was used to estimate the dose of PAD required to prevent sensitisation in the D negative recipients. The calculation was adapted to consider the presence of organ donor D positive adult RBCs in the circulation of recipients instead of, larger, fetal RBCs.

Samples from 20 patients, all female, aged 14-53 years (one 2-year-old outlier) were referred from 2016 to September 2020. The transplants were-liver (n = 6), kidney (n = 6) and lung (n = 8). D positive cell populations were identified in 11 cases (0.1-8.0 ml); and required PAD (500-1500 IU). From these 20 patients, 10 sent a follow-up sample, where 8 required PAD top-up due to the detection of residual D positive cells (0.1-2 ml)-liver (n = 1), kidney (n = 1) and lung transplant (n = 6).

All patients in the study were D negative females, in which 18 were considered by guidelines to be of childbearing potential (2-42 years old) and 2 were >50 years old. Referrals demonstrate an awareness for the correct calculation of PAD to prevent D sensitisation. The sample size is small, but top up requirement in 8/20 of cases demonstrates accurate quantification is clearly needed to ensure the appropriate dose of PAD is provided.