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To summarize the literature regarding the role of the serum free light chain (SFLC) assay in diagnosis as an adjunct to traditional tests (defined as serum and urine electrophoresis or immunofixation electrophoresis), compared with traditional testing alone, and its role compared with traditional tests in the management of patients with plasma cell dyscrasias (PCDs).
MEDLINE®, the Cochrane Central Register of Controlled Trials, and the Cochrane Database of Systematic Reviews from January 2000 through January 2012.
We used established systematic review methods, selecting only published, peer-reviewed, English-language articles on the basis of predetermined eligibility criteria. A standardized protocol was used to extract details on designs, diagnoses, interventions (diagnostic tests/disease monitoring), outcomes, and study methods. We considered studies of adults with suspected and diagnosed PCDs, specifically monoclonal gammopathy of undetermined significance (MGUS) or multiple myeloma (MM), which includes light chain MM, nonsecretory MM, and AL amyloidosis. The comparison and outcomes of interest were the role of the SFLC assay as an adjunct to traditional tests for diagnosis of PCDs, and the effectiveness of the SFLC assay versus traditional tests for studying progression to MM, treatment response, and prognosis.
The literature search yielded 3,036 citations, with 2,711 excluded at the abstract level. The remaining 325 articles were retrieved for full-text review, upon which 310 were excluded, most often because studies did not meet all the predefined eligibility criteria or were not comparative. A total of 15 studies were included. Three retrospective, fair-quality studies evaluated the SFLC assay as an adjunct to traditional testing in populations suspected of having a PCD. Three retrospective, poor-quality studies of AL amyloidosis, and eight studies (three of fair quality and five of poor quality) of MM, six of which were retrospective, evaluated either baseline or post-treatment concentrations of SFLC or monoclonal protein as predictors of clinical outcomes. Overall, because of the small number of studies and their poor methodological quality and considerable clinical heterogeneity, the strength of evidence was rated as insufficient regarding: (1) the value of adjunct SFLC testing on diagnostic accuracy in undiagnosed patients, (2) the role of the SFLC assay as a better predictor of outcome in PCDs or of progression of MGUS to MM, and (3) the role of the SFLC assay as a better indicator for therapeutic decisionmaking compared with traditional testing alone and as a substitute for other diagnostic tests.
The role of the SFLC assay remains to be defined. The evidence was rated as insufficient to suggest that the assay may increase sensitivity when used as an adjunct to traditional testing for diagnosis of PCDs or that it was more effective for predicting and monitoring treatment response and for predicting patient survival. Methodological limitations of the studies reviewed preclude definitive conclusions regarding these potential uses. Future research should focus on standardization of diagnostic testing and monitoring algorithms in prespecified patient populations, with adherence to accepted definitions of outcomes and responses.