The International Myeloma Working Group reported criteria for making the diagnosis of light chain MGUS (Monoclonal Protein of Undetermined Significance).

Criteria for light chain MGUS - all of the following:

(1) abnormal kappa-to-lambda ratio

(1a) excessive kappa light chains with kappa-to-lambda ratio > 1.65

(1b) excessive lambda light chains with kappa-to-lambda ratio < 0.26

(2) no immunoglobulin heavy chain expression on immunofixation

(3) urinary monoclonal protein < 500 mg per 24 hours

(4) clonal bone marrow plasma cells  < 10%

(5) no evidence of end-organ damage attributable to the light chain disorder

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