Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 15 3 2021 07 14 152 159 Fatemeh Zamani Department of Pathology, Shahid Faghihi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran Mansoureh Shokripour Department of Pathology, Shahid Faghihi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran Maral Mokhtari Department of Pathology, Shahid Faghihi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran 2020 01 05 2020 04 21 Background: Multiple myeloma is a hematologic malignancy manifested by the secretion of abnormal immunoglobulin. Different methods have been described for diagnosis and patient response to management. Serum free light-chain assay is recently approved in the diagnosis of multiple myeloma patients. This study aimed to evaluate the diagnostic accuracy of serum free light-chain assay and its agreement to bone marrow findings. Materials and Methods: Forty-six patients with the diagnosis of multiple myeloma were enrolled in the study. The patients were grouped into newly diagnosed cases (22 patients,47.8%) and known cases who were under treatment (24 patients,52.2%). Bone marrow study was done and percentage and clonal status of plasma cells were evaluated by a combination of immunohistochemistry and flow cytometry. Free light-chain assay was done in all patients and sensitivity, specificity, positive predictive value, and negative predictive value were analyzed. Results: Thirty of 46 patients showed monoclonal plasma cell infiltration and 16 patients showed polyclonal plasma cell infiltration based on bone marrow findings. An abnormal κ/λ ratio was seen in 15(68.18%) of new cases and 16(66.6%) of known cases. Sensitivity, specificity, PPV and NPV for κ⁄λ ratio were 72.73%, 46.15%, 71%, and 50%, respectively. Conclusion: In conclusion, due to high false positive and false negative results, the presence of an abnormal serum FLC ratio was not equal to the presence of monoclonal gammopathy, and observation of a normal ratio does not exclude the presence of monoclonal gammopathy. https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/1251 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/1251/880