These guidelines  discuss published data that provides evidence for the utility and application of sFLC assays for most plasma cell disorders, including symptomatic MM, nonsecretory MM (NSMM), light chain MM (LCMM), SMM, MGUS, solitary plasmacytoma and AL amyloidosis. Furthermore, the guidelines highlight key recommendations for the use of sFLC assays in screening, prognosis and in the assessment of patient response to treatment. Specific emphasis is placed on distinguishing between proven utility and those potential utilities that remain under investigation.
sFLC assays are recommended for use in combination with serum protein electrophoresis (SPE) and serum immunofixation electrophoresis (sIFE) to screen for pathological monoclonal plasma cell proliferative disorders although if AL amyloidosis is suspected, a 24-hour urine, immunofixation electrophoresis (uIFE) should also be performed.
It is recommended that baseline sFLC assay results are obtained at diagnosis for all patients with MGUS, SMM or active MM, solitary plasmacytoma and AL amyloidosis. Highly abnormal results have prognostic value in virtually every plasma cell disorder. Notably, in MGUS, SMM and plasmacytoma, a highly abnormal sFLC ratio indicates a substantial risk of progression to systemic disease.
Monitoring and response assessment
sFLC assays are recommended for the quantitatitve monitoring of patients with oligosecretory plasma cell disorders, including patients with AL amyloidosis, oligosecretory myeloma, and in nearly two-thirds of patients previously classified as having NSMM. Furthermore, in the absence of urinary evaluations or FLC measurements, light chain escape can be missed and so these tests should be performed periodically. Baseline results of sFLC testing are required prior to initiating new chemotherapy regimens for all patients with MM to determine if a stringent complete response has been attained after a complete response has been achieved. Despite limited published data validating the use of sFLC assays in patients with light chain deposition disease, it is stated that the personal experience of the guideline authors confirms their utility in these cases.