Evaluation of Serum Free Light Chain in Diagnosis and Monitoring of Plasma Cell Disorders

Abstract

To determine diagnostic accuracy of serum free light chain assay compared to serum and urine protein electrophoresis in plasma cell disorders. Descriptive cross-sectional study. This study was conducted in the Immunology Department, Armed Forces institute of Pathology (AFIP), Rawalpindi, from May 2017 to May 2018. Patients referred to AFIP for diagnosis of plasma cell disorders or for monitoring while receiving treatment were included in study. They were tested for serum protein electrophoresis (SPE), urine protein electrophoresis (UPE), immunofixation (IF), and serum free light chain assay (sFLC). IF was used as the reference standard. Test results were compared in terms of sensitivity, specificity, positive or negative predictive value, and accuracy index. During the study period 220 patients were tested for plasma cell disorders. One hundred and sixty-seven patients tested positive. One hundred twenty-nine patients had multiple myeloma, 13 plasmacytoma, 11 monoclonal gammopathy of undetermined significance, 6 amyloidosis, 6 POEMS, and 2 Waldenstrom macroglobulinemia. SPE had a sensitivity of 70.5%, specificity of 100%; sFLC had a sensitivity of 87%, specificity of 81%; and UPE had a sensitivity of 23.5%, specificity of 97%. Accuracy index was 80.5% for SPE, 85% for sFLC, and 54% for UPE. When taken together, SPE and UPE had a combined sensitivity of 72%, specificity 97%, and accuracy index 80.5%. SPE and sFLC had combined sensitivity of 98.6%, specificity 84.3%, and accuracy index 94%. Combination of SPE and sFLC had the highest sensitivity and accuracy index for diagnosis and monitoring of plasma cell disorders compared with conventional tests.