Estimation of the allowable total error of the absolute CD34+ cell count by flow cytometry using data from UK NEQAS exercises 2004-2024.

Objectives: The knowledge of the measurement uncertainty (MU) of a diagnostic laboratory test is essential to keep the reliability of laboratory results under control, is requested by regulatory bodies, and for the clinician to be aware of the grey zone of variability around the reported values. The calculation of the percent allowable total error (%aTE) defines the levels of acceptable and optimal MU for each measurand. The CD34+ hemopoietic precursor cell level in blood, as a flow cytometric measurand, still lacks reliable MU and %aTE indicators.

Methods: %aTE of the absolute count of CD34+ cells in stabilized peripheral blood has been evaluated using a UKNEQAS database of 69,294 valid results entries from the Stem Cell Enumeration EQA/PT Programme over the last 20 years. The state-of-the-art (SOTA) desirable performance achievable by 80 % of participants and the optimal performance by the best laboratories were calculated at four levels of absolute CD34+ cell counts, from 0 to 10 to >50 cells/μL.

Results: Double platform users displayed worse %aTE as compared to single platform users in both periods, with a general trend to improvement with time. Single platform users in the 2014-2024 decade performed best, with a flat %aTE trend over the years. The SOTA-based %aTE were calculated for each method and every decision-making cell level, showing relatively narrow ranges.

Conclusions: Our EQA/PT study with stabilized peripheral blood CD34+ cell suspensions reliably estimated the %aTE of the absolute CD34+ cell count, mostly related to the purely analytical variability and devoid of the preanalytical interferences caused by the decay of fresh samples.