OA4-AM24-ST-13 - Residual Red Blood Cells (rRBC) and Microparticles (MP) in Apheresis Platelet Products

The number of rRBC in platelet products is of interest due to concerns related to alloimmunization. Current guidelines recommend that RhD-negative (D-) patients receive platelets from D- donors, however inventory limitations make this challenging. Studies have shown exposure of ≥0.03mL (approx. 300x10⁶) RBCs is sufficient to develop antibodies following incompatible transfusions. This study investigated the number of rRBCs and MP in apheresis platelets (AP) to establish the associated risk of alloimmunization.

Study

Design/Methods:

AP (Trima, Terumo BCT) in 100% plasma (N=335) were tested for rRBC on a Sysmex XN hematology analyzer. ADAM testing was used for residual WBC (rWBC) counts. 195 samples were obtained from routine quality control (QC), including products flagged by the AP device requiring follow-up testing. The remaining 140 samples were collected from AP independent of QC testing. Additionally, flow cytometry (BD FACSLyric) was used to characterize RBC MP content using CD235a antibody (Biolegend) and sizing beads (160-800nm, Bang Labs Megamix) in AP (N=9), and apheresis plasma (N=20). Pre-donation peripheral blood and subsequent AP from two additional donors were also evaluated.

Results/Findings:

There were 17 samples with rRBC >10x10⁶ (mean 29.4, max 127.8), 14 originating from flagged AP requiring QC. Seven of these 14 samples had rWBC ≥5x10⁶ and were discarded, including the AP with 127.8x10⁶ rRBC. The remaining 7 flagged samples had rRBC 10-62x10⁶ and 3 unflagged samples contained < 15 x10⁶ rRBCs. In all other components (N=318), mean rRBC was 0.5±1.2x10⁶. A notable correlation was detected between rWBC failures and high rRBCs (P < 0.0001,R2=0.08). Mean RBC MP concentration was 21.5±5.1x10³/μL for AP (range 13-30 x10³/μL) and 6.4±1.6x10³/μL in apheresis plasma (range 4-16 x10³/μL). Peripheral blood MP content prior to an AP collection was 7.6±2.1x10³/μL and in the subsequently collected platelet product 21.0±0.7x10³/μL. The majority of CD235+ MP were < 500nm.

Conclusions:

The risk of alloimmunization from rRBC in AP platelets is extremely low, and the majority of products with elevated rRBC levels were flagged by the Trima device. Data was fitted to a gamma distribution model, which predicted a 0.2% [0.02%, 1%] (95% Confidence Interval) probability for a single apheresis platelet unit containing enough rRBC for alloimmunization (0.03 mL or 300x10⁶). Significantly more MP were detected in AP compared to plasma products (p < 0.001). RBC MP are smaller but more numerous than rRBCs, and alloimmunization potential of such small particles has not been established.