Urine protein electrophoresis (UPEP) identifies the presence of monoclonal light chains in the urine (Bence Jones proteinuria). If only light chains are produced, they don’t accumulate in the serum (because they are rapidly catabolized by the kidneys), and a 24-hour UPEP is needed. The results of the 24-hour urine collections are less affected by the dilution or concentration of the random collections, as determined by the hydration status. The normal ratio of kappa to lambda chains is 2:1. Urinary excretion of monoclonal light chains in MM alters this ratio.

The dipstick tests commonly used for screening for proteinuria are not useful in myeloma, because the indicator dye tetrabromophenol binds mainly to albumin, and do not detect light chains. Of note, significant albuminuria suggests coexisting amyloidosis.

Quantification of the M spike in the urine is important in patients with light chain myeloma, especially when monitoring the disease status. The example below shows the development over time of an M spike in the urine electrophoresis of a patient with multiple myeloma, consistent with disease progression (left side = remission, right side = relapse).






The kappa and lambda chains of the immunoglobulin molecules can be bound to the heavy chains (forming the intact immunoglobulins), but they can also be found as free light chains in the serum, because they are usually produced in excess. They are filtered freely by the renal glomeruli, due to their low molecular weight (22.5 kDa for kappa, and 45 kDa for lambda).

The free light chain (FLC) assay uses antisera directed against epitopes that are exposed only when the light chains are free, i.e., not bound to the heavy chains. The FLC assay is useful for the diagnosis and monitoring of multiple myeloma. It allows the detection of monoclonal proteins in some patients with non-secretory myeloma and primary AL amyloidosis that were previously undetectable. The FLC assay provides a much greater sensitivity than older methods, such as the immunofixation, which can detect free light chains at a minimum concentration of 100-150 mg/L. It is particularly useful in light chain myeloma. There is a good correlation between serum FLC levels and daily light-chain urinary excretions, and this test is more convenient than the 24-hour urine collection and analysis, which is often cumbersome and prone to inaccuracy.

Due to the short half life of free light chains (approximately 3-4 hours), the FLC assay can provide a rapid indication of the response to treatment.


Practical considerations for the measurement of free light chains in serum.
Clin Chem. 2003 Aug;49(8):1252-7.
Tate JR, Gill D, Cobcroft R, Hickman PE.

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):246-8.
Alyanakian MA, Abbas A, Delarue R, Arnulf B, Aucouturier P.

Clinical usefulness of free light chain concentration as a tumor marker in multiple myeloma.
Ann Hematol. 2005 Sep;84(9):588-93.
Kang SY, Suh JT, Lee HJ, Yoon HJ, Lee WI.

Serum free light chain analysis and urine immunofixation electrophoresis in patients with multiple myeloma.
Clin Cancer Res. 2005 Dec 15;11(24 Pt 1):8706-14.
Nowrousian MR, Brandhorst D, Sammet C, Kellert M, Daniels R, Schuett P, Poser M, Mueller S, Ebeling P, Welt A, Bradwell AR, Buttkereit U, Opalka B, Flasshove M, Moritz T, Seeber S.

The evolving use of serum free light chain assays in haematology.
Br J Haematol. 2008 May;141(4):413-22.
Pratt G.

The relationship between the serum free light chain assay and serum immunofixation electrophoresis, and the definition of concordant and discordant free light chain ratios.
Blood. 2009 Jul 2;114(1):38-9.
Singhal S, Vickrey E, Krishnamurthy J, Singh V, Allen S, Mehta J.
This study explores the relationship between serum free light chain assay (FL) and serum immunofixation electrophoresis (IFE) in 2648 serial samples from 122 patients with IgG or IgA multiple myeloma. Surprisingly, the results were often discordant, as FL was normal in 34% of cases with positive IFE, and abnormal in 31% of cases with negative IFE.

Comparison of serum immunofixation electrophoresis and free light chain assays in the detection of monoclonal gammopathies.
Clin Lymphoma Myeloma Leuk. 2010 Aug 1;10(4):278-80.
Wood PB, McElroy YG, Stone MJ.

Comparison of serum free light chain and urine electrophoresis for the detection of the light chain component of monoclonal immunoglobulins in light chain and intact immunoglobulin multiple myeloma.
Haematologica. 2016 Mar;101(3):356-62.
Dejoie T, Attal M, Moreau P, Harousseau JL, Avet-Loiseau H.
This study compared results of FLC and UPEP in 182 myeloma patients. As expected, there was an agreement between results of FLC and UPEP, but the FLC assay was more sensitive than the UPEP for monitoring response to therapy.

Serum free light chains, not urine specimens, should be used to evaluate response in light-chain multiple myeloma.
Blood. 2016 Dec 22;128(25):2941-2948.
Dejoie T, Corre J, Caillon H, Hulin C, Perrot A, Caillot D, Boyle E, Chretien ML, Fontan J, Belhadj K, Brechignac S, Decaux O, Voillat L, Rodon P, Fitoussi O, Araujo C, Benboubker L, Fontan C, Tiab M, Godmer P, Luycx O, Allangba O, Pignon JM, Fuzibet JG, Legros L, Stoppa AM, Dib M, Pegourie B, Orsini-Piocelle F, Karlin L, Arnulf B, Roussel M, Garderet L, Mohty M, Meuleman N, Doyen C, Lenain P, Macro M, Leleu X, Facon T, Moreau P, Attal M, Avet-Loiseau H.
This is a study that prospectively compared results of serum and urine specimen in the context of the 2009 IFM myeloma trial. The authors showed that in 113 patients with light chain myeloma, serum free light chains (FLC) were superior to urine methods (UPEP and uIFE) in the monitoring the response to therapy. Serum FLC had superior sensitivity and prognostic value. At baseline, FLC were abnormal in 100% of patients, whereas a measurable urine M component (>200 mg/24 hours) by UPEP was observed in only 64% of cases. After 3 cycles of chemotherapy, serum FLC remained elevated in 46% of patients, and urine M only in 18% (and all patients with positive UPEP had elevated serum FLC). The authors concluded that urine tests underestimated the amount of FLC production, and overestimated the response to chemotherapy. Progression-free survival after 3 cycles of chemotherapy was shorter in patients with elevated serum FLC, but not with positive UPEP or uIFE. Serum FLC levels are preferred over urine FLC, which are more erratic, presumably because of the variable urine excretion rate of the FLC among different individuals. 





The Hevylite assay indicates the ratio of monoclonal to isotype matched polyclonal immunoglobulins.


Prognostic utility of intact immunoglobulin Ig'κ/Ig'λ ratios in multiple myeloma patients.
Leukemia. 2013 Jan;27(1):202-7.
Bradwell A, Harding S, Fourrier N, Mathiot C, Attal M, Moreau P, Harousseau JL, Avet-Loiseau H.

Immunoglobulin heavy/light chain ratios improve paraprotein detection and monitoring, identify residual disease and correlate with survival in multiple myeloma patients.
Leukemia. 2013 Jan;27(1):213-9.
Ludwig H, Milosavljevic D, Zojer N, Faint JM, Bradwell AR, Hübl W, Harding SJ.

Comparison of Hevylite™ IgA and IgG assay with conventional techniques for the diagnosis and follow-up of plasma cell dyscrasia.
Ann Clin Biochem. 2015 May;52(Pt 3):337-45.
Paolini L, Di Noto G, Maffina F, Martellosio G, Radeghieri A, Luigi C, Ricotta D.

Heavy/light chain specific immunoglobulin ratios provides no additional information than serum proteins electrophoresis and immunofixation for the diagnosis and the follow-up of intact immunoglobulin multiple myeloma patients.
Pathol Biol (Paris). 2015 Sep;63(4-5):215-21.
Beaumont-Epinette MP, Moreau C, Besnard S, Latute F, Collet N, Sebillot M, Grosbois B, Bendavid C, Guenet L, Decaux O.

Involved/uninvolved heavy/light chain index can predict progression in transplanted multiple myeloma patients.
Bone Marrow Transplant. 2017 Aug;52(8):1206-1207.
Espiño M, Arteche-López A, Medina S, Muñoz-Calleja C, Blanchard MJ, Alegre A, López-Jiménez FJ, Villar LM.



Giampaolo Talamo, M.D.