Serum free light chain (FLC) assay is a test to detect abnormal levels of free light chains in the serum. The test is reported as individual kappa and lambda free light chain results with a ratio that can be used to support a diagnosis of a plasma cell disorder. The serum FLC assay involves the binding of antibodies to light chains when they are free but not when they are bound to heavy chains in intact immunoglobulin molecules. Abnormalities of the free light chain ratio (kappa/lambda) provide a more sensitive indication of monoclonal disease than simple elevations of one light chain. This is because a plasma cell tumor will usually express a surplus of one light chain but also suppress the production of the alternate light chain. FLC testing is now recommended for the initial evaluation of suspected myeloma; for prognosis of plasma cell dyscrasias; and for monitoring oligosecretory myeloma and AL amyloidosis.

If the patient has a cryoprotein, specimen MUST BE DRAWN AND KEPT WARM AT 37°C UNTIL AFTER PROCESSING IS COMPLETE.

Before collection, pre-warm a red top tube (e.g., in an infant heel warmer). Have another infant heel warmer on hand to deliver the blood to the laboratory after collection. Keep specimen at 37°C by wrapping a hot pack (infant heel warmer) around the tube immediately after collection. Transport specimen to laboratory within 10 minutes of collection. Contact laboratory if unable to assure delivery within 10 minutes.

Centrifuge. Transfer cell-free serum to plastic vial. Refrigerate.

IMPORTANT: IF THE PATIENT HAS A CRYOPROTEIN, keep blood specimen at 37°C during entire processing procedure. Place collection tube in the 37°C incubator for two hours. Spin tube at 1730 G-force for 10 minutes at 37°C. Remove spun serum to labeled tube. Place WARM sticker on tube and refrigerate.

Centrifuge. If a complete barrier has not formed, transfer cell-free serum to plastic vial. Refrigerate.

IF THE PATIENT HAS A CRYOPROTEIN, specimen MUST be collected and processed using the Collection and Specimen Processing procedures above prior to transport. Write WARM on the tube and transport specimen with coolant pack after processing is complete.

Transport specimen to laboratory. Transport with coolant pack if coming from clinic location.

IF THE PATIENT HAS A CRYOPROTEIN, transport blood specimen to laboratory within 10 minutes of collection. Keep specimen at 37°C by wrapping tube in a hot pack (infant heel warmer). Specimen MUST be processed using the Specimen Processing procedure above prior to transport if coming from clinic location. Write WARM on the tube and transport specimen with coolant pack after processing is complete.

Grossly hemolyzed samples are not acceptable.

Reference interval: 0 days to 9 years-- No reference interval available

10 years and up:

Reference intervals apply to individuals with normal renal function.  

The specificity of this assay for detection of monoconal light chains relies on the ratio of free kappa and lambda light chains. Once an abnormal FLC K/L ratio has been demonstrated and a diagnosis has been made, the quantitation of the monoclonal light chain is useful for monitoring disease activity.

Changes in FLC quantitation reflect changes in the size of the monoclonal plasma cell population. Experience to date is limited, but changes of >25% or trending of multiple specimens are needed to conclude biological significance.

It is not recommended that serum free light chains are ordered to assess for multiple myeloma or light chain disease in the setting of inflammatory conditions or renal insufficiency.  Serum free light chains (both kappa and lambda) rise in inflammatory conditions and renal insufficiency.   The absolute levels may be elevated; however, the ratio will be normal.  For questions, contact the Immunology Laboratory at 608-263-6207.