B-068 Reference Intervals for Serum Free Light Chains when Ruling out Monoclonal Gammopathies in Subjects with Normal or Minimally Variant Electrophoretic Findings

Abstract

Abstract Background Serum free light chains (SFLC) analysis for detection and initial diagnosis of monoclonal gammopathies (MC) is a critical tool in the comprehensive assessment of risk and in management of established disease. Our reference intervals (RIs) for SFLC were based on the seminal report by Katzmann. Recent literature indicates with current analytic platforms and reagent formulations, significantly different RIs might be more appropriate. Methods The study sought to establish RIs for the population typically evaluated for possible MC and was expected to include acute/chronic inflammation, polyclonal elevations of gamma-globulins, hypogammaglobulinemia and chronic liver disease. The reference population inclusion criteria were: serum submitted for a serum monoclonal protein evaluation and SPE (± IFIX); lacked any direct or indirect evidence of a MC; normal or minimally variant SPE pattern; no prior history of leukemia, lymphoma, myeloma or MGUS; normal eGFR (CKD1–2 or >60 mL/min). CKD-EPI calculation was based only on IDMS-standardized creatinine measurements without race modifiers. Of the 202 cases encountered over 15 days, 135 met the inclusion criteria. Specimens were tested using a Binding Site Optilite system. Results The mean subject age was 62 years. There was a mild female predominance (80 females vs 55 males) and females tended to be younger than males (58 vs 68 years). Two approaches used to establish the central 95% interval (mean ± 2SD and ranked-order analysis for 2.5 and 97.5 percentiles) yielded similar limits for SFLC and SFLC ratio (Table). These results agree well with recent reports from others. Conclusion As international guideline prognostic thresholds for SFLCR in plasma cell neoplasia are based upon the original Binding Site free light chain analysis, we will maintain those RIs, adding an appended comment to all SFLC reports to indicate for screening purposes, the HFH laboratory-established SFLC ratio interval is 0.8–1.9:1.