Evaluation of Serum Kappa Free Light Chain Reference Interval Using a New Stabilized Calibrator

Area of Science:

• Clinical Chemistry
• Immunodiagnostics
• Hematology

Background:

• Serum free light chains (FLC), including kappa FLC and lambda FLC, are crucial for diagnosing and monitoring plasma cell disorders.
• Concerns about upward drift in kappa FLC measurements led to a reformulated calibrator by The Binding Site.
• This study evaluates the impact of the new kappa FLC calibrator on reference intervals and diagnostic ranges.

Purpose of the Study:

• Assess the effect of a reformulated kappa FLC calibrator on kappa FLC reference interval (RI).
• Evaluate the impact on the diagnostic range of the kappa to lambda FLC ratio.
• Determine if the new calibrator aligns with manufacturer-suggested intervals and diagnostic ranges.

Main Methods:

• Serum samples from 124 healthy volunteers were analyzed using both new and prior kappa FLC calibrators on an Optilite analyzer.
• Capillary electrophoresis screened for monoclonal proteins, and creatinine was measured to assess renal function.
• Kappa FLC values and FLC ratios were compared between the two calibrator lots.

Main Results:

• Minimal differences were observed in kappa FLC values between the new and prior calibrators.
• Neither calibrator allowed for verification of the manufacturer-suggested kappa FLC RI in the study population.
• The proportion of participants within the FLC ratio diagnostic range (0.26-1.65) was similar for both calibrators, with 6-7% exceeding the upper limit.

Conclusions:

• The reformulated kappa FLC calibrator does not validate the manufacturer's claimed kappa FLC RI.
• The new calibrator did not increase the number of healthy individuals within the FLC ratio diagnostic range.
• Reevaluation and updating of kappa FLC RI and FLC ratio diagnostic ranges in consensus guidelines are recommended.