Free Light Chains (Blood)

Diagnostic Use

Initial investigation for monoclonal gammopathy:
Free light chains (FLCs) should be requested when screening for plasma cell disorders:
• Any process that increases immunoglobulin synthesis, or decreases clearance, will increase free light chains.
• Polyclonal gammopathy (e.g. from inflammation/infection) will usually increase both kappa and lambda proportionally, so the ratio is expected to be normal.
• Monoclonal gammopathy will increase only one of kappa or lambda, producing an abnormal ratio.
• Less commonly, biclonal gammopathy may occur, increasing both kappa and lambda.
• Chronic kidney disease may be associated with a mild rise in kappa FLC, lambda FLC and the kappa/lambda ratio.
Rarely, extremely high concentrations of a free light chain may cause a falsely low result (antigen excess). This can be resolved by contacting the laboratory to perform additional dilution.
Monitoring of known monoclonal gammopathy:
FLC assays are useful for monitoring amyloidosis, light chain myeloma and non-secretory myeloma. Additionally, FLCs are cleared more rapidly than intact immunoglobulins (half life is hours vs. weeks), so FLCs can be useful for monitoring acute response to treatment.
FLC testing is costly so should not be used for routine monitoring in most patients with a quantifiable paraprotein band in the serum. Paraprotein band quantitation by capillary electrophoresis is more accurate and costs less.
When monitoring a plasma cell disorder that does not have a measurable protein band on electrophoresis. The frequency will depend on the acuity, in a patient receiving active treatment, once monthly is maximum recommended. In stable MGUS, 6 -12 monthly may be sufficient.
Individual FLCs can be ordered separately to reduce testing cost. This can be done by specifying the single light chain type, e.g. “serum free light chain – kappa”. This is recommended when there is a known gammopathy of only one free light chain. Note that a ratio cannot be reported in this case.

Limitation in serial monitoring:
Due to method limitations, there may be some variability in results when sample dilution is required.
Due to manufacturing limitations, some analytical drift (10-15%) can occur over time. Every effort is made by our staff to minimise the impact on results.
Some variation in measured FLC concentrations is expected between laboratories, especially those using a different analytical method. Ideally the same lab should be used for serial FLC monitoring.
Rarely, extremely high concentrations of a free light chain may cause a falsely low result (antigen excess). This can be resolved by contacting the laboratory to perform additional dilution.

Reference Intervals