Comprehensive Assessment of Flow Cytometry Light Chains: Qualitative and Quantitative Evaluation Using Serum Protein Immunofixation and Free Light Chain Analysis

BACKGROUND: The detection of Kappa (κ) and Lambda (λ) light chains is crucial for the diagnosis and management of diseases such as multiple myeloma. Abnormal secretion of κ and λ light chains can be assessed quantitatively or qualitatively using various methods. This study aimed to compare the outcomes of κ and λ light chains and their ratio (κ/λ) in different patients with and without monoclonal gammopathies, utilizing flow cytometry, serum free light chain assays, and gel immunofixation. METHODS: This retrospective study included data from 92 patients, both with and without monoclonal gammopathy. Patients were categorized into two groups based on serum protein electrophoresis and immunofixation: those with positive monoclonal bands (n = 77) and those without (n = 15). Simultaneous assessments of bone marrow plasma cells were conducted using flow cytometry, along with serum free κ and λ light chain assays. RESULTS: After natural logarithm transformation, the serum κ/λ ratio was compared to the flow cytometry results for plasma cells. The κ/λ ratios showed a stronger association between serum free light chains and abnormal plasma cells (r = 0.84, p < 0.001) compared to normal plasma cells (r = 0.32, p < 0.05). Additionally, chi-squared analysis indicated a significant association for detecting free light chains for flow cytometry in comparison to serum immunofixation technique (p < 0.001) with sensitivity and specificity of 94.2% and 47.6% respectively. CONCLUSION: Free light chain immunophenotyping using flow cytometry can serve as a complementary technique for identifying the type and quantity of positive free light chains in conjunction with immunofixation and serum free light chain assays.