Serum Free Light Chain (FLC) Analysis: A Guiding Light in Monoclonal Gammopathy Management

Comparison of 24-hour versus random urine samples for determination and quantification of Bence Jones protein in a South African population

Background

The International Myeloma Working Group and College of American Pathologists recommend a 24-h urine collection to determine the Bence Jones protein (BJP) excretion level for monitoring treatment response in patients with multiple myeloma (MM). There are several issues related to sample collection and the method is prone to inaccuracy.

Objective

This study compared measured 24-h to random urine collections for the quantitation of BJP in a South African population.

Methods

Sixty-six patients with MM submitted random urine samples with their routine 24-h urine collection from April 2016 – March 2018. Measured 24-h urine BJP was compared to two estimated 24-h BJP excretions calculated as follows: Estimation 1 (E1): Estimated 24-h BJP (mg/24 h) = Urine BJP/Creatinine ratio (mg/mmol) × 10. Estimation 2 (E2): Estimated 24-h BJP (mg/24 h) = Urine BJP/Creatinine ratio (mg/mmol) × 15 mg/kg for women or × 20 mg/kg for men.

Results

Correlation of estimation equations E1 and E2 to the measured 24-h urine BJP was 0.893. Patients showed no difference in classification of treatment response using either the E1 or E2 estimation equations when compared to the measured 24-h urine BJP results.

Conclusion

This study demonstrates that the estimated 24-h BJP shows a high degree of correlation with the measured 24-h BJP and can likely be used to monitor treatment response in South African patients with MM.

Evaluation of Correlation between Serum Free Light-Chain Assay and Bone Marrow Study in Multiple Myeloma Patients

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.