Differential diagnosis of lymphocytosis in routine laboratory practice: the contribution of Sysmex- XN9100

Background: This study investigates the possibility of distinguishing clonal lymphocytosis from non-neoplastic lymphocytosis by using some of the data provided by the haematology analyzer XN9100 (RDW-SD, PLT, LYMPH#, IG#, HFLC %, LY-X). Materials and methods: Data from 161 samples with lymphocyte counts between 4.00 and 20.00x10^9/L were initially analysed, 90 of which were diagnosed with non-malignant lymphocytosis (NON LPD) and 71 with malignant lymphocytosis CLL, lymphoma and ALL (LPD) from the analysis of the ROC curves. For two parameters of equal significance (e.g. LINFO% and LINFO# in absolute value or RDW-SD and RDW-CV), that with greater discriminatory power was selected according to p-value and are under the curve (AUC). The selected parameters were assessed using multiparametric logistic regression, with only non- redundant data included, as they were even more useful (than the single parameter) in distinguishing the two groups. Results: The logistic regression equation resulting from the statistical analysis with MEDCALC and ANALYSE-IT is: logit (GROUP) = 57.3 - 0.07799 RDW-SD + 0.01244 PLT - 0.6164 LYMPH# - 39.18 IG# + 1.403 HFLC % -0.644 LY- X. If this formula is applied to the results of each sample, a "score" is obtained which, when the ROC curves are evaluated, gives an AUC value of 0.976. With a score value >1.5, only 1 sample with malignant lymphocytosis was identified as “non-malignant” (specificity 98.6 %). Of the 90 non-malignant samples, 73 were correctly classified and 17 were classified as suspected malignant. The "performance" of the score in terms of specificity was further verified by inserting the data of new samples to be assigned to the corresponding group into a spreadsheet. 107 of the 116 samples analyzed with lymphocytes between 4.00 and 20.00x10^9/L were correctly identified, 6 viral infections were false positives and only three were false negatives. Conclusions: This study shows that Sysmex-XN9100 may help in the differential diagnosis of lymphocytosis.