The use of serum free light chain dimerization patterns assist in the diagnosis of AL amyloidosis.

The discrimination between benign and malignant forms of plasma cell dyscrasia (PCD) is often difficult. Free light chain monomer-dimer pattern analysis (FLC-MDPA) may assist in solving this dilemma and distinguish between AL amyloidosis and benign PCD. Serum samples of patients with AL amyloidosis and benign PCD were analysed in a blinded manner. Quantitative Western blotting was performed to estimate dimerization and clonality indices, and thereby determine the source of the tested samples, as derived either from benign or malignant PCD. The findings obtained by the FLC-MDPA were compared with the actual diagnosis. Of 37 samples from patients with active AL amyloidosis, 34 (91·9%) fulfilled dimerization criteria for diagnosis of AL amyloidosis. Of the 45 samples from patients with benign PCD, 10 (21·2%) tested falsely positive or gave an inconclusive result. Thus, the sensitivity of the analysis was 92·5% with a remarkable negative predictive value of 91·9%. In addition, of 20 patients who were in complete or very good partial remission, only one tested positive. By multivariate analysis, FLC-MDPA was the best independent marker predicting AL amyloidosis (odds ratio of 84). The FLC-MDPA offers a highly effective tool in the diagnostic assessment of patients with PCD.