Among residents of Olmsted County, Minnesota, MGUS was found in 3.2 percent of persons 50 years of age or older and 5.3 percent of persons 70 years of age or older.

Monoclonal gammopathy of undetermined significance (MGUS) is a premalig-

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Background: The detection of monoclonal free light chains (FLCs) is an important diagnostic aid for a variety of monoclonal gammopathies and is especially important in light-chain diseases, such as light-chain myeloma, primary systemic amyloidosis, and light-chain-deposition disease. These diseases are more prevalent in the elderly, and assays to detect and quantify abnormal amounts of FLCs require reference intervals that include elderly donors. Methods: We used an automated immunoassay for FLCs and sera from a population 21–90 years of age. We used the calculated reference and diagnostic intervals to compare FLC results with those obtained by immunofixation (IFE) to detect low concentrations of monoclonal κ and λ FLCs in the sera of patients with monoclonal gammopathies. Results: Serum κ and λ FLCs increased with population age, with an apparent change for those >80 years. This trend was lost when the FLC concentration was normalized to cystatin C concentration. The ratio of κ FLC to λ FLC (FLC K/L) did not exhibit an age-dependent trend. The diagnostic interval for FLC K/L was 0.26–1.65. The 95% reference interval for κ FLC was 3.3–19.4 mg/L, and that for λ FLC was 5.7–26.3 mg/L. Detection and quantification of monoclonal FLCs by nephelometry were more sensitive than IFE in serum samples from patients with primary systemic amyloidosis and light-chain-deposition disease. Conclusions: Reference and diagnostic intervals for serum FLCs have been developed for use with a new, automated immunoassay that makes the detection and quantification of monoclonal FLCs easier and more sensitive than with current methods. The serum FLC assay complements IFE and allows quantification of FLCs in light-chain-disease patients who have no detectable serum or urine M-spike.

Background-Monoclonal gammopathy of undetermined significance (MGUS) is a common premalignant plasma cell disorder defined by evidence of immunoglobulin heavy chain (IgH expression). MGUS is the precursor lesion for most cases of multiple myeloma (MM), but up to 20% of MM is characterized by complete lack of IgH expression; the prevalence of a corresponding precursor entity, light chain MGUS (LC-MGUS) is unknown.

A small proportion of PSC patients had elevated serum IgG4. In these patients parameters of liver disease severity were more pronounced and time to liver transplantation was shorter, suggesting a more severe disease course. It is possible that this subset of patients behaves similarly to autoimmune pancreatitis patients with biliary strictures, and could potentially respond to corticosteroids. Testing PSC patients for IgG4 and treating those with elevated levels with corticosteroids in clinical trials should be considered.

BACKGROUND The repertoire of serologic tests for identifying a monoclonal gammopathy includes serum and urine protein electrophoresis (PEL), serum and urine immunofixation electrophoresis (IFE), and quantitative serum free light chain (FLC). Although there are several reports on the relative diagnostic contribution of these assays, none has looked at the tests singly and in combination for the various plasma cell proliferative disorders (PCPDs). METHODS Patients with a PCPD and all 5 assays performed within 30 days of diagnosis were included (n = 1877). The diagnoses were multiple myeloma (MM) (n = 467), smoldering multiple myeloma (SMM) (n =191), monoclonal gammopathy of undetermined significance (MGUS) (n = 524), plasmacytoma (n = 29), extramedullary plasmacytoma (n = 10), Waldenström macroglobulinemia (WM) (n = 26), primary amyloidosis (AL) (n = 581), light chain deposition disease (LCDD) (n =18), and POEMS syndrome (n = 31). RESULTS Of the 1877 patients, 26 were negative in all assays. Omitting urine from the panel lost an additional 23 patients (15 MGUS, 6 AL, 1 plasmacytoma, 1 LCDD), whereas the omission of FLC lost 30 patients (6 MM, 23 AL, and 1 LCDD). The omission of serum IFE as well as urine lost an additional 58 patients (44 MGUS, 7 POEMS, 5 AL, 1 SMM, and 1 plasmacytoma). CONCLUSIONS The major impact of using a simplified screening panel of serum PEL plus FLC rather than PEL, IFE, and FLC is an 8% reduction in sensitivity for MGUS, 23% for POEMS (7 patients), 4% for plasmacytoma (1 patient), 1% for AL, and 0.5% for SMM. There is no diminution in sensitivity for detecting MM, macroglobulinemia, and LCDD.