Objective: To determine the normal range, reference intervals and diagnostic ranges of serum free light chains (sFLC) and to evaluate the clinical significance of serum sFLC in diagnosis of multiple myeloma (MM).
Methods: Peripheral blood samples were collected from 63 healthy persons and 72 MM patients, including 35 cases of kappa-MM and 37 cases of lambda-MM. Immuno-turbidimetry and immunofixation electrophoresis (IFE) were used to detect the serum sFLC and monoclonal element of FLC. The specificity and sensitivity of sFLC were evaluated by comparing the results with those obtained by IFE.
Results: (1) The 95% reference interval for sFLC of the healthy persons was (9 - 29) mg/L, and that for sFLC-lambda was (15 - 34) mg/L. The diagnostic interval for sFLCkappa/lambda of the healthy persons was 0.59, and the 100% reference interval was 0.27 - 2.49. (2) The 95% reference intervals for sFLC-kappa and sFLC-lambda of the kappa-MM patients were (53 - 14 100) mg/L and (0 - 97) mg/L respectively, and those of the lambda-MM patients were (9 - 117) mg/L and (205 - 6875) mg/L respectively. The interval for sFLCkappa/lambda of the kappa-MM and lambda-MM patients were 10.27 and 0.005 respectively. (3) In the healthy persons sFLC-kappa and sFLC-lambda levels were positively correlated with age (P = 0.031 and P = 0.01), however, such correlation did not exist in the MM patients. No correlation between sFLCkappa/lambda and age was found in both the healthy persons and MM patients (both P > 0.05). (4) Detection and quantification of monoclonal FLC by nephelometry were more sensitive than IFE in serum samples from the patients with MM.
Conclusion: The reference interval and diagnostic range of sFLC in Chinese have been obtained. Quantification of sFLC proves useful in the diagnosis and monitoring of patients with MM.