During the process of transplantation of hematopoietic stem cells (HSCs) from venous blood cell count is usually performed before stem cell collection (apheresis) in venous blood and after apheresis procedure in apheresis products. Enumeration of HSCs is performed by flow cytometry according to the protocol suggested by International Society of Hematotherapy and Graft Engineering. For research purposes, hematology analyzers upgraded with a channel for the determination of immature cells can also be used. The purpose of this dissertation was to determine the agreement between the two methods of measurement and to determine in which cases analyses performed by flow cytometry could be replaced by analyses on hematology analyzer. We wanted to suggest changes in decision-making scheme that could help make clinical decisions more accurate and faster. In the experimental part, venous blood samples, fresh and frozen apheresis products' samples were analysed by both methods using flow cytometer and hematology analyzer. Statistical analyses of the results were performed by MedCalc statistical software. All three groups of the analysed samples were treated separately, as well as venous blood samples with very low leucocyte concentration (? 3 × 109/L) in which HSC concentration is not determined according to the established decision criteria. Correlation between the two methods was assessed using Spearman's correlation coefficient both for percentages and concentrations of HSCs. We observed a very strong correlation in the group of all analysed samples (N = 179), in venous blood samples (N = 103) and in fresh apheresis products' samples (N = 56), and a weak correlation in venous blood samples with very low leucocyte concentration (N = 12) and in frozen apheresis products' samples (N = 20). Bland-Altman analysis confirmed that the results of analyses with both methods agreed very well in venous blood and fresh apheresis products, but there was a poor agreement between methods in venous blood with low leucocyte concentration and in frozen apheresis products. Hematology analyzer could be used to substitute most of the analyses of venous blood samples performed with flow cytometer to determine the optimal starting point of apheresis. In venous blood samples with very low leucocyte concentration analyses by hematology analyzer could be introduced and the results, in cases of high levels of HSCs, confirmed with flow cytometer. In spite of a good agreement between the methods, fresh apheresis products are always analysed by flow cytometry because the amount of HSCs in a transplant is crucial for a successful transplantation.
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