New Reference Values Proposed for Serum Free Light Chain Levels and Ratio for Patients with Chronic Kidney Disease

Serum free light chains (FLC) play an important role in detection, prognosis, and monitoring of monoclonal gammopathies. However, they are dependent on kidney function, which can vary between patients, and no kidney reference exists for kappa or lambda.

Thorir Einarsson Long, MD, PhD and colleagues screened 75,422 patients from the Iceland Screens, Treats or Prevents Multiple Myeloma (iStopMM) by serum protein electrophoresis (SPEP) and serum immunofixation (IFE) in addition to serum FLC assay and creatinine level.

They further analyzed the subset of 6503 patients with eGFR < 60 mL/min/1.73 m2 and without evidence of monoclonality on SPEP or IFE and found with current reference intervals, 60% of participants had values outside the normal range for kappa and 21% for lambda. In addition, the FLC ratio was outside the standard reference interval in 9% of participants and outside the kidney reference interval in 0.6%. Based on these findings, the researchers developed proposed new reference levels for kappa, lambda, and FLC ration based on kidney function.