Free ? and ? Light Chains Plus Ratio, Quantitative, Urine

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Turnaround Time: 2 - 4 days
CPT Code:


Test Type: 1.5 mL Urine (random or 24-hour)
Stability Time:

Stable at room temperature 25°C for seven days or refrigerated at 2°C to 8°C for four weeks; longer when frozen at -20°C or lower.

Reference Range:


• Free κ light chains: 0.63−113.79 mg/L

• Free λ free light chains: 0.47−11.77 mg/L

• κ:λ free light chain ratio: 1.03–31.76


Immunoglobulin molecules consist of two identical heavy chains (α, δ, ε, γ, or μ) which define the immunoglobulin class and two identical light chains (κ or λ). Each light chain is covalently linked to a heavy chain and the two heavy chains are linked covalently at the hinge region. In healthy individuals, the majority of light chains in serum exists in this form, bound to heavy chain; however, low levels of free light chain (FLC) are found in serum of normal individuals due to the overproduction and secretion of FLC by the plasma cells. While the molecular weight of both light chains is approximately 22.5 kilodaltons, in serum, κ free light chain (κ-FLC) exists primarily as a monomer and λ free light chain (λ-FLC) as a covalently-linked dimer with a molecular weight of approximately 45 kilodaltons. This will lead to a differential glomerular filtration rate for κ-FLC and λ-FLC and may explain the observed ratio of κ-FLC to λ-FLC of 0.625 in serum compared to the ratio of bound κ to λ of 2.0.

The laboratory will perform FLC analysis on urine, but a serum sample is preferred for many reasons. Analogous to glucose metabolism, FLC spill into the urine only after the tubular reabsorptive capacity is exceeded. Thus, the serum FLC ratio has been shown to be abnormal in patients with monoclonal gammopathy despite normal urine FLC ratios or normal urine immunofixation. Serum tests are also more sensitive for the detection of residual monoclonal FLC after treatment and for the early detection of monoclonal FLC after relapse in patients with monoclonal gammopathy.

FLC levels in urine are normally low. In a healthy kidney, the tubular cells selectively reabsorb all FLC so their presence in urine is probably due to secretion into the urinary tract.

The appearance of higher levels of polyclonal FLC in urine may be indicative of kidney or autoimmune disease. An abnormal urine FLC ratio may be indicative of malignant lymphoproliferative disease such as multiple myeloma. The monoclonal urinary FLC associated with lymphoid malignancy is called a Bence-Jones protein.

Alyanakian MA, Abbas A, Delarue R, et al. Free immunoglobulin light-chain serum levels in the follow-up of patients with monoclonal gammopathies: correlation with 24-hr urinary light-chain excretion. Am J Hematol. 2004 Apr; 75(4):246-248. PubMed 15054820

Bradwell AR, Carr-Smith HD, Mead GP, et al. Highly sensitive, automated immunoassay for immunoglobulin free light chains in serum and urine. Clin Chem. 2001 Apr; 47(4):673-680. PubMed 11274017

Cole PW, Durie BGM, Salmon SE. Immunoquantitation of free light chain immunoglobulins: Applications in multiple myeloma. J Immunol Methods. 1978; 19(4):341-349. PubMed 416145

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 May 1; 97(9):2900-2902. PubMed 11313287

Katzmann JA, Clark RJ, Abraham RS, et al. Serum reference intervals and diagnostic ranges for free kappa and free lambda immunoglobulin light chains: Relative sensitivity for detection of monoclonal light chains. Clin Chem. 2002 Sep; 48(9):1437-1444. PubMed 12194920

Mösbauer U, Ayuk F, Schieder H, Lioznov M, Zander AR, Kröger N. Monitoring serum free light chains in patients with multiple myeloma who achieved negative immunofixation after allogeneic stem cell transplantation. Haematologica. 2007 Feb; 92(2):275-276. PubMed 17296589

Nowrousian MR, Brandhorst D, Sammet C, et al. Serum free light chain analysis and urine immunofixation electrophoresis in patients with multiple myeloma. Clin Cancer Res. 2005 Dec 15; 11(24):8706-8714. PubMed 16361557

Pescali E, Pezzoli A. The clinical spectrum of pure Bence Jones proteinuria. A study of 66 patients. Cancer. 1988 Dec 1; 62(11):2408-2415. PubMed 3179959

Solling K, Solling J, Romer FK. Free light chains of immunoglobulins in serum from patients with rheumatoid arthritis, sarcoidosis, chronic infections and pulmonary cancer. Acta Med Scand. 1981; 209(6):473-477. PubMed 6266206

Tang LX, Showell P, Carr-Smith HD, et al. Evaluation of F(ab')(2)-based latex-enhanced nephelometric reagents for free immunoglobulin light chains on the Behring Nephelometer™ II. Clin Chem. 2000; 46:(6 Suppl):705, pA181. PubMed 11274017

Collection Details:

Collection Instructions:

Values obtained with different assay methods should not be used interchangeably in serial testing. It is recommended that only one assay method be used consistently to monitor each patient's course of therapy. This procedure does not provide serial monitoring; it is intended for one-time use only.

Plastic urine container.

Ship the specimen as soon as possible.

Stable at room temperature 25°C for seven days or refrigerated at 2°C to 8°C for four weeks; longer when frozen at -20°C or lower.