Free Light Chains, Serum

Test Identifier Information

End-point Nephelometry: - Latex particles are coated with protein specific anti-human antibodies (e.g. anti-free kappa or anti-free lambda) forming antigen:antibody complexes, when exposed to serum containing that specific protein. The latex particles improve sensitivity by increasing the turbidity of the antigen:antibody complex in solution. Quantitative nephelometric measurement of the turbidity is proportional to the concentration of the protein in the serum. Serum protein concentrations can then be calculated by comparing the turbidity to that of a known standard. (Individual light chains are assayed separately and the ratio of kappa to lambda subsequently calculated.)

The Serum Free Light Chains (SFLC) test is useful for:

• Monitoring of light chain monoclonal gammopathies
• Monitoring gammopathies where the heavy chain is of insufficient concentration to assay.

The anti-sera used in this test is specific to light chains not bound to heavy chains. Excessive levels of free light chains in the serum is therefore strongly supportive of light chain involvement. The serum free light chains test is more sensitive than immnuofixation especially where patients may have:

• Non-secretory multiple myeloma (NSMM)
• Primary systemic amyloidosis (AL)
• Light chain depostion disease (LCDD)

If differential diagnoses include multiple myeloma then the following tests should also be considered:

• Serum Protein Profile (SPE) with Immunofixation
• Bence-Jones Proteins (Urine)
• Beta2-Microglobulin

Specimen Collection

NOTE: Moderate to marked lipaemic samples may interefere with analysis

Instructions for Referral to CHLabs

CHLabs Laboratory

 NOTE: Considerable care should be exercised in the interpretation of results.

In the first instance, the kappa:lambda ratio should be examined to determine the involved light chain. (The involved light chain is the dominant light chain.)

The kappa:lambda ratio may appear normal if:

• Both kappa and lambda light chains are elevated (such as in polyclonal hypergammaglobulinaemia or uncommon biclonal gammopathies)
• The patient is suffering from renal failure. The kappa:lambda ratio may be normal or slightly elevated.

An abnormal kappa:lambda ratio may be found in:

• Amyloidosis (AL)
• Myeloma (MM)
• Monoclonal gammopathy of uncertain significance (MGUS)
• Light chain myeloma (LCMM)
• Non-secretory myeloma (NSMM)

If a patient has been diagnosed with an abnormal kappa:lambda ratio, it is important to monitor the level of the involved light chain over several tests to determine whether the general trend in results is stable, increasing, or decreasing.

The MAYO Clinic has also observed that, in their experience, a change of >25% in the involved light chain quantitation may also be of biological significance.

Whilst sensitive, this test is subject to considerable variability, especially if not analysed in the one laboratory (up to 50%). It is therefore strongly recommended that monitoring of a patient be performed through one laboratory and the results of several tests be reviewed to determine the overall picture.

Refer to Protein Chemistry Lab Ext 80334.