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Free light chains

Category Biochemistry >> Proteins
Test background

The haematological neoplasms that arise through primarily tumours of the B-cell haematopoietic lineage and subsequent plasma cells comprise a wide range of disorders that include the multiple myelomas, Waldenström’s macroglobulinaemia, AL amyloidosis (primary systemic amyloidosis), heavy chain disease and the plasmacytomas. Disease is typically characterised by secretion of monoclonal immunoglobulins, their free light chain components or fragments thereof, and diagnosis and staging of disease progression often employs the systematic assay of these specific proteins over time.

NWLP Serum Electrophotesis Free Light Chain Interpretation Local Guidance 2023
Clinical Indications

Serum FLC assay is of greater clinical utility than urinary BJP assay in diagnosis of non-Ig secretory multiple myeloma. Stratification of risk for development of multiple myeloma in MGUS cohorts. Staging of established malignancy Assessment of response to chemotherapeutic intervention (especially with regard to AL amyloidosis, light chain and non-secretory multiple myeloma). Prognostic indicator/tumour marker for detection of residual tumour or cancer recurrence.

It is recommended that serum protein electrophoresis and serum free light chains (sFLC) are used to determine the presence of a paraprotein, which may indicate possible myeloma or monoclonal gammopathy of undetermined significance (NG35). Approximately 20% of cases of myeloma do not have a detectable intact immunoglobulin: do not use serum protein electrophoresis, sFLC or BJP alone to exclude a diagnosis of myeloma.

BJP analysis may prove useful where there are marginally increases/decreases in the serum free light chain ratio.

Reference range

Free Kappa chains: 3.3-19.4 mg/L Free Lambda chains: 5.7-26.3 mg/L

Kappa:Lambda ratio:0.26-1.65

For impaired renal function: sFLC Ratio reference range is 0.37 to 3.10

Sample & container required SST (gold top) or serum (red top)
Sample volume 0.5 mL
Transport storage Stable at 2-8°C for 72 hours. Please freeze pending dispatch for analysis. Sample can be sent by first class post.
Turnaround time 1 week

Grossly haemolysed samples are unsuitable for this assay.

Serum Free Light Chain Local Guidance:

  • sFLC ratio ≤0.01 or ≥100: Myeloma related event (MRE), requiring urgent referral
  • Abnormal sFLC ratio in MGUS indicates higher progression risk
  • sFLC ratio ≤0.125 or ≥8 in smouldering/asymptomatic myeloma: increased progression risk


sFLC Ratio  Action
≥100 or ≤0.01 Meets criteria for symptomatic myeloma

Urgent referral to Haematology

>10 or <0.1 Abnormal serum free light chain ratio. Suggest referral and/or discussion with Haematology
0.1 – 0.2


5 – 10

Mildly abnormal serum free light chain ratio. ?Possible Light Chain only MGUS, amyloidosis or other light chain disorder. Suggest discuss with Haematology
0.2 – 0.25


1.66 – 5

Likely minor abnormality of sFLC. If normal serum electrophoresis, likely causes may include inflammation or impaired renal function. Consider measurement of urine Bence Jones protein
For impaired renal function: sFLC Ratio reference range is 0.37 to 3.10