Serum Free Light Chain Assessment in 311 Patients with Gammopathy.

Serum free light chain (FLC) levels are a useful multiple myeloma (MM) marker and a indicator of tumour burden both for diagnosis and follow up purposes. A total of 311 patient samples were assayed in our laboratory for FLC and the kappa/lambda (κ/λ) chain ratio was calculated and compared with the classical methods for characterization of gammopathy (immunofixation, IMF, immunoglobulin levels and total light chain levels and respective ratio). Ig (A, G, M) and total κ and λ chain levels were assayed by nephlometry (Dade-Behring BNII). Immunofixation was performed in a Hydrasys (Sebia) setting. FLC assay was done using Binding Site reagents (Dade-Behring). Statistical analysis was performed by SPSS® for Windows v. 15. Concordance between IMF results and free κ/λ chain ratio was calculated. Sensitivity and specificity of the free κ/λ chain ratio in the identification of positive and negative IMF were also determined. Reference intervals used for free κ/λ and total κ/λ chain ratios were [0.26; 1.65] and [1.35; 2.65], respectively. Out of 311 patients with gammopathy studied, 235 had absence of monoclonality as defined by the immunoelectrophoretic profile. Inclusively, only 51% of the 53 patients with suspected MM and 66% of the 41 patients with a diagnosis of MGUS were IMF positive. Sensitivity and specificity of total κ/λ chain ratio for identification of positive or negative IMF were respectively 70% and 91% with a global concordance of 86%. In 215 (70%) patients, IMF and free κ/λ chain ratio were in agreement. However, 74 (32%) of IMF negative patients had abnormal free κ/λ chain ratio: 18% had a final diagnosis of chronic renal failure, 13% of CLL or NHL, 9% of MGUS, 7% of MM and 3% of amyloidosis; the remainder 50% were diagnosed as having a disease other than lymphoplasmacytic disorder. These results stress the value of free light chain determination in the diagnosis and follow up of gammopathies and its usefulness as a marker for multiple myeloma and associated monoclonal gammopathies.