Evaluation of the Flagging Performance of the Hematology Analyzer Sysmex XN Series on the Basis of "Q Values''

초록

Context.-In the XN series of hematology analyzers (Sysmex, Kobe, Japan), the probability of the presence of abnormal cells is indicated by flags based on Q values. Objective.-To evaluate the Q value performance of the Sysmex XN-20 modular analyzer. Design.-The interinstrumental concordance, intrainstrumental precision, and diagnostic accuracy of Q values, with tested flags of "blasts/abnormal lymphocytes,'' "atypical lymphocytes,'' and "blasts,'' were investigated. Results.-Absolute concordance rates in flagging between 2 analyzers ranged from 69.8% to 80.8%, and j values ranged from 0.43 to 0.61. In samples with absolute related cell counts lower than 100/lL, the values ranged from 0.31 to 0.52. For intrainstrumental precision, standard deviations ranged from 4.8 to 23.9 for the blasts/abnormal lymphocytes, from 18.7 to 59.1 for the blasts, and from 11.0 to 23.0 for the atypical lymphocytes. Using a default Q value cutoff, diagnostic accuracy values based on the area under the curve, sensitivity, and specificity were, respectively, 0.910, 90.9%, and 72.2% for blasts/abnormal lymphocytes; 0.927, 84.9%, and 89.8% for blasts; and 0.865, 74.4%, and 84.9% for atypical lymphocytes. The diagnostic accuracy of Q values was much lower in samples with absolute related cell counts lower than 100/lL than in those 100/lL or higher. Conclusions.-Q values of the Sysmex XN-20 analyzer were found to be imprecise and irreproducible, especially with samples containing a small number of pathologic cells. Adjustments in the Q value threshold may help in the detection of these cells.