Differential diagnosis of lymphocytosis in routine laboratory practice: Contribution of lymphocyte parameters using the Sysmex‐XN9000 haematology analyzer

This study investigates the potential contribution of structural and dispersion parameters, as well as alarms provided by Sysmex XN9000 haematology analyzer. The objective was to assess the need for a microscopic examination in the context of lymphocytosis. It also aims to contribute in differentiating rapidly lymphoproliferative disorders such as chronic lymphocytic leukaemia (CLL), non-chronic lymphocytic leukaemia (NON-CLL) and non-infectious reactive lymphocytosis (REAC).We prospectively assessed lymphocyte parameters (Ly-X, Ly-Y, Ly-Z, Ly-WX, Ly-WY, Ly-WZ) provided by the Sysmex XN9000 analyzer; they were measured in the white blood cell differential (WDF) channel which also provides alarms via the precursor/pathological cellular channel (WPC). Blood samples from 71 subjects with CLL, NON-CLL lymphoproliferative and REAC non-infectious reactive lymphocytosis, as well as a control (NORM) group of 12 subjects without any abnormalities were analyzed.The most discriminating parameters to distinguish the different groups were Ly-X, Ly-Z and Ly-WZ. The lymphoid structural parameters Ly-X and Ly-Z significantly discriminated the CLL group from the other groups (p < 0.001), and the CLL group from the REAC group (p < 0.01), respectively. The Ly-WZ parameter discriminated the CLL group from the NON-CLL, REAC (p < 0.001) and NORM (p < 0.01) groups. Alarms were higher in all study groups compared to the NORM group. An algorithm integrating these structural and alarm parameters is proposed.This study demonstrated that Ly-X, Ly-Z, and Ly-WZ lymphocyte parameters are useful for detecting morphological changes in lymphocytes; they provide useful information for the differential diagnosis of lymphocytosis, and this before the examination of the blood smear. An algorithm combining the WDF (parameters) and the WPC (alarms) makes it possible to decide whether or not to use a microscopic examination or flow cytometry immunophenotyping.