Summary Introduction Hematology analyzers should optimize flagging while minimizing false‐negative results and unnecessary microscopic reviews. Methods We compared flagging performance of Sysmex XE‐5000 and XN analyzers in oncohematologic patients. Differential counts were performed by Cellavision digital system (100 cells) and a hematologist (another 100 cells). Results First, we included 292 samples (86 with blasts): 28 acute lymphoblastic leukemia, 88 acute myeloid leukemia, 91 myelodysplastic syndromes, 45 chronic myeloproliferative neoplasms, and 40 chronic myelomonocytic leukemia. Sensitivity, specificity and efficiency to detect blasts were 59.3%, 88.3%, and 79.8% for XE‐5000 analyzer and 70.9%, 91.3%, and 85.2% for the XN analyzer. Then, we included 111 lymphoid malignancies. In 55 CLL XE‐5000 flagged for Abn Lympho/L_Blasts?, XN flagged for Abn Lympho?. In one‐third of 19 samples with splenic marginal lymphoma, none of the analyzers flagged. In 5 Sézary syndrome cases, XE‐5000 triggered the Abn Lympho/L_Blasts? flag while the flagging in XN was less consistent: Abn Lympho? Blasts? and Atypical Lympho?. In 5 hairy cell leukemias, both analyzers only flagged one sample. In 13 myelomas, XE‐5000 generated Atypical Lympho? flag; XN triggered more variable flags. In other lymphoid malignancies, flags were variable. XN analyzer generates less samples with false basophilia. Conclusion XN analyzer has improved blast detection in oncohematologic patients. Operators cannot rely on the blast flag alone but have to consider other flags and hemogram data. In lymphoproliferative disorders, XN analyzer yields less samples with pseudobasophilia. Both analyzers must improve flagging for hairy cell leukemia.