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Test Code FLCS Immunoglobulin Free Light Chains, Serum


Specimen Required


Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL serum

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.


Useful For

Monitoring serum from patients with monoclonal light chain diseases without a M-protein.

 

May be useful as a diagnostic test in patients in whom there is a suspicion of primary systemic amyloidosis, light chain deposition disease, or non-secretory myeloma

Profile Information

Test ID Reporting Name Available Separately Always Performed
KFLCS Kappa Free Light Chain, S No Yes
LFLCS Lambda Free Light Chain, S No Yes
KLRS Kappa/Lambda FLC Ratio No Yes

Testing Algorithm

The following algorithms are available:

-Amyloidosis: Laboratory Approach to Diagnosis

-Multiple Myeloma: Laboratory Screening

Method Name

Turbidimetry

Reporting Name

Immunoglobulin Free Light Chains, S

Specimen Type

Serum

Specimen Minimum Volume

Serum: 0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 28 days
  Frozen  28 days
  Ambient  72 hours

Reference Values

KAPPA-FREE LIGHT CHAIN

0.33-1.94 mg/dL

 

LAMBDA-FREE LIGHT CHAIN

0.57-2.63 mg/dL

 

KAPPA/LAMBDA FLC RATIO

0.26-1.65

Interpretation

The specificity of this assay for detection of monoclonal light chains relies on the ratio of free kappa and lambda (K/L) light chains. Once an abnormal free light chain (FLC) K/L ratio has been demonstrated and a diagnosis has been made, the quantification 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. Our experience to date is limited, but changes of more than 25% or trending of multiple specimens are needed to conclude biological significance.

Clinical Reference

1. Kaleta E, Kyle R, Clark R, Katzmann J. Analysis of patients with gamma-heavy chain disease by the heavy/light chain and free light chain assays. Clin Chem Lab Med. 2014;52(5):665-669. doi:10.1515/cclm-2013-0714

2. Palladini G, Russo P, Bosoni T, et al. Identification of amyloidogenic light chains requires the combination of serum-free light chain assay with immunofixation of serum and urine. Clin Chem. 2009;55(3):499-504. doi:10.1373/clinchem.2008.117143

3. Dispenzieri A, Kyle R, Merlini G, et al. International Myeloma Working Group guidelines for serum-free light chain analysis in multiple myeloma and related disorders. Leukemia. 2009;23(2):215-224. doi:10.1038/leu.2008.307

4. Drayson M, Tang LX, Drew R, Mead GP, Carr-Smith H, Bradwell AR. Serum free light-chain measurements for identifying and monitoring patients with nonsecretory multiple myeloma. Blood. 2001;97(9):2900-2902

5. Bertamini L, Alberge JB, Lee DJ, et al. Serum free light chains in a racially diverse population including African Americans and populations from South Africa. Blood. 2025;145(8):840-849

6. Farnsworth CW, Roemmich B, Spears GM, Murray DL, Dispenzieri A, Willrich MAV. Clinical specificity of two assays for immunoglobulin kappa and lambda free light chains. Clin Chem Lab Med. 2023;62(5):929-938

7. Rozenova K, Willrich M, Snyder M, et al. Kappa free light chain drift prompts the need for a new upper limit of normal free light chain ratio to avoid an epidemic of kappa light chain monoclonal gammopathy of undermined significance. J Appl Lab Med. 2023;8(4):742-750

8. Fink SL, Wener MH, Rudolf JW, et al. A universal reference interval for serum immunoglobulins free light chains may be outdated. Clin Chem Lab Med. 2023;61(11):e229-e232

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

83521 x 2

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FLCS Immunoglobulin Free Light Chains, S 104533-5

 

Result ID Test Result Name Result LOINC Value
LFLCS Lambda Free Light Chain, S 33944-0
KLRS Kappa/Lambda FLC Ratio 104546-7
KFLCS Kappa Free Light Chain, S 104544-2

Day(s) Performed

Monday through Friday

Report Available

1 to 3 days

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-General Request (T239)

-Hematopathology/Cytogenetics Test Request (T726)

-Renal Diagnostics Test Request (T830)

-Kidney Transplant Test Request