Abstract:Objective To investigate the application and significance of membrane surface immunoglobulin M (sIgM) in the differential diagnosis of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). Methods The clinical data of 420 first-confirmed CLL patients and 67 MCL patients admitted to the Hematology Department of Jiangsu Provincial People's Hospital from May 2016 to August 2022 were retrospectively collected. Among CLL patients, there were 298 cases of typical immunophenotype CLL (tCLL) and 122 cases of atypical immunophenotype CLL (aCLL). Multiparametric flow cytometry (MFC) was used to detect the expression levels of sIgM and the recognized CLL diagnostic immunomarker CD200 in tumor cells of all patients, and the differential diagnostic value of sIgM, CD200 and their combination in aCLL and MCL was analyzed. Results The high expression rates of sIgM decreased sequentially in MCL (88.1%), aCLL (23.0%), and tCLL (8.7%)（χ²=193.218, P＜0.01); On the contrary, the high expression rates of CD200 increased sequentially in MCL (10.4%), aCLL (78.7%), and tCLL (92.9%)（χ²=261.194, P＜0.01). The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of sIgM in differentiating MCL and aCLL were similar to those of CD200. Compared with the single indicator of CD200 or sIgM, the sIgM combined with CD200 had higher diagnostic sensitivity (98.5%) and negative predictive value (98.7%). Conclusion The sIgM expression level has a good clinical application value in the diagnosis of CLL and MCL, especially in the differential diagnosis of aCLL and MCL.