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HelpTest ID: 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:
Special Instructions
Method Name
Turbidimetry
Reporting Name
Immunoglobulin Free Light Chains, SSpecimen Type
SerumSpecimen Minimum Volume
Serum: 0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 28 days |
| Frozen | 28 days | |
| Ambient | 72 hours |
Clinical Information
The monoclonal gammopathies are characterized by a clonal expansion of plasma cells that secrete a monoclonal immunoglobulin. The monoclonal immunoglobulin secreted by these cells serves as a marker of the clonal proliferation, and the quantification of monoclonal protein can be used to monitor the disease course. The monoclonal gammopathies include multiple myeloma (MM), light chain MM (LCMM), Waldenstrom macroglobulinemia (WM), nonsecretory MM (NSMM), smoldering MM (SMM), monoclonal gammopathy of undetermined significance (MGUS), primary systemic amyloidosis (AL), and light chain deposition disease (LCDD). The monoclonal light chain diseases (LCMM, AL, LCDD, and NSMM) often do not have serum monoclonal proteins in high enough concentration to be detected and quantitated.
An elevated ratio of kappa to lambda free light chains (FLC K/L) indicates a monoclonal kappa FLC, and an abnormally low FLC K/L indicates a monoclonal lambda FLC. The kappa and lambda FLC may both be elevated in the sera of patients with polyclonal hypergammaglobulinemia, but the FLC K/L is normal. If a patient has an abnormal serum FLC K/L ratio but has no serum monoclonal protein detected by immunofixation, a urine monoclonal protein study (eg, immunofixation) should be performed and the serum immunofixation should be repeated.
The FLC K/L ratio may be useful as a diagnostic test for patients in whom immunofixation for serum monoclonal light chains is negative and in whom there is a suspicion of primary systemic amyloidosis, light chain deposition disease, or non-secretory myeloma.
The quantification of kappa or lambda immunoglobulin free light chains may be used to monitor disease activity in patients with monoclonal light chain diseases without a serum M-spike.
The following algorithms are available:
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
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 daysForms
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)
mml-myeloma-amyloidosis-dysprotenemia