Specialized Testing

Free Light Chains (Serum)

Serum Free Light Chain (SFLC) analysis is used to quantitatively measure the levels of free kappa and lambda light chains in the serum. An abnormal SFLC ratio may indicate the presence of a paraprotein. It can be more sensitive for detection of light-chain-only malignancies that often are not detected by standard serum and urine protein electrophoresis and immunofixation studies. However, the serum free light chain ratio can be elevated due to decreasing renal function or inflammation, thus an abnormal serum free light chain ratio does not establish the presence of a paraprotein. Conversely, a normal serum free light chain ratio does not entirely exclude a paraprotein. Therefore, results must be interpreted in the context of electrophoresis and immunofixation results as well as clinical findings.

SFLC ratio is also useful for serial monitoring of patients, and as a prognostic marker, with elevated ratios predicting higher chance of progression from MGUS to malignant disease. Additionally, a SFLC ratio of greater than 100 (abnormal light chain to normal light chain) has recently been listed as an additional criterion for the diagnosis of symptomatic plasma cell myeloma.

Order names:

  • PEP AN [5004425]- Initial screening includes SPEP. Reflex test may include immunofixation and serum free light chain analysis.
  • PEP NO AN [5002125]- SPEP only, There will not be SFLC or additional reflex testing.
  • Free Light Only [6907201]- SFLC for disease monitoring.


If you have any questions or concerns, please contact Dr. Caitlin Schein at (918)744-2553 or Patti Loykasek, MT(ASCP) SC at (918)744-2500 or 1-800-722-8077 or email caitlin.schein@ascension.org or patti.loykasek@ascension.org.