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Serum free light chains (kappa/lambda)

Protein Electrophoresis · also called sFLC, FLC ratio, Kappa/lambda ratio

What it measures

Measures kappa and lambda light chains circulating unbound to heavy chains and their ratio. Used to screen for and monitor myeloma, light-chain disease and AL amyloidosis.

Specimen and preparation

Specimen: Serum
Tube: Gold top

Reference range

Group	Range
Free kappa	3.3–19.4 mg/L
Free lambda	5.7–26.3 mg/L
Kappa/lambda ratio	0.26–1.65
Ratio, renal impairment	0.37–3.1

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

Abnormal ratio: light-chain myeloma or other plasma cell neoplasm
AL amyloidosis
Both chains raised with normal ratio: kidney disease or inflammation

Causes of low values

Suppressed uninvolved chain in myeloma
Immunodeficiency

Method

Nephelometric or turbidimetric immunoassay with free-light-chain-specific antibodies

Good to know

An involved/uninvolved ratio of 100 or more with involved chain ≥100 mg/L is a myeloma-defining event. Assays from different makers are not interchangeable.

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