Impact of Pre-Analytical and Analytical Variables Associated with Sample Preparation on Flow Cytometric Stainings Obtained with EuroFlow Panels.

Objective interpretation of FC results may still be hampered by limited technical standardization. The EuroFlow consortium conducted a series of experiments to determine the impact of different variables on the relative distribution and the median fluorescence intensity (MFI) of markers stained on different cell populations, from both healthy donors and patients' samples with distinct hematological malignancies. The use of different anticoagulants; the time interval between sample collection, preparation, and acquisition; pH of washing buffers; and the use of cell surface membrane-only (SM) vs. cell surface plus intracytoplasmic (SM+CY) staining protocols, were evaluated. Our results showed that only monocytes were represented at higher percentages in EDTA- vs. heparin-anticoagulated samples. Application of SM or SM+CY protocols resulted in slight differences in the percentage of neutrophils and debris determined only with particular antibody combinations. In turn, storage of samples for 24 h at RT was associated with greater percentage of debris and cell doublets when the plasma cell disorder panel was used. Furthermore, 24 h storage of stained cells at RT was selectively detrimental for MFI levels of CD19 and CD45 on mature B- and T-cells (but not on leukemic blasts, clonal B- and plasma cells, neutrophils, and NK cells). The obtained results showed that the variables evaluated might need to be tailored for sample and cell type(s) as well as to the specific markers compared; however, defining of well-balanced boundaries for storage time, staining-to-acquisition delay, and pH of washing buffer would be a valid recommendation for most applications and circumstances described herein.

Frequent issues and lessons learned from EuroFlow QA.

EuroFlow Quality Assessment was designed to provide a feedback on the quality of the standardization effort in executing the EuroFlow protocols for sample preparation and instrument setup. It was first beta-tested by the members of the EuroFlow consortium internally (2010-2013) and opened to the external participants from 2015 onwards. The goal of participation in the EuroFlow QA is to evaluate whether the technical quality of the data generated by the laboratory is comparable to the data of the EuroFlow members and thus if a non-EuroFlow member participant can use the EuroFlow reference sample database for his own patient evaluation. Also it assesses whether data are sufficiently standardized for automated population gating and alarm notification. By spring 2018, a total 87 laboratories from 32 countries on five continents have registered for the EuroFlow QA program. We evaluated 163 results of 2015-2016 QA rounds, where we noted clear improvement in the score of first-time participants (median score of 91% correct) when they participated second time or later (median score of 94% correct, p = 0,017), which was comparable to EuroFlow member scores (median score of 97% correct). Among frequent mistakes, we found non-adherence to the EuroFlow protocols (improper reagent used), improper gating and some compensation issues. In summary, we show that EuroFlow QA has a positive impact on improvement of standardized data quality of non-member laboratories adhering to the EuroFlow standard operating procedures and reagent panels.