Allowable total error in CD34 cell analysis by flow cytometry based on state of the art using Spanish EQAS data.

Objectives: CD34+ hematopoietic stem cell (HSC) enumeration, crucial for HSC transplantation, is performed by flow cytometry to guide clinical decisions. Variability in enumeration arises from biological factors, assay components, and technology. External quality assurance schemes (EQAS) train participants to minimize inter-laboratory variations. The goal is to estimate total error (TE) values for CD34 cell enumeration using state-of-the-art (SOTA) methods with EQA data and to define quality specifications by comparing TE using different cutoffs.

Methods: A total of 3,994 results from 40 laboratories were collected over 11 years (2011-2022) as part of the IC-2 Stem Cells Scheme of the GECLID Program that includes absolute numbers of CD34 cells. The data were analyzed in two periods: 2011-2016 and 2017-2022. The TE value achieved by at least 60 %, 70 %, 80 %, and 90  % of laboratories was calculated across the two different periods and at various levels of CD34 cell counts: above 25, 25 to 15, and under 15 cells/μL.

Results: A decrease in the SOTA-based TE for CD34 cell enumeration was observed in the most recent period in 2017-2021 compared with 2012-2016. A significant increase of P75 TE values in the low CD34 range (<15 cells/μL) levels was found (p<0.001).

Conclusions: Technical advancements contribute to the decrease TE over time. The TE of CD34 cell FC counts is measure-dependent, making it responsive to precision enhancement strategies. The TE measured by EQAS in this study may serve as a quality specification for implementing ISO 15189 standards in clinical laboratories for CD34 cell enumeration.