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Free Light Chains
(a.k.a Serum Free Light Chains, SFLC, sFLC)
minimum sample volume required ~ 5ml
Test Code: FLC
Tube type: SST
Other acceptable tube types
None
Special instructions
Request as part of an initial myeloma screen (in place urine BJP).
Minimum retesting interval: 3 months (unless specifically advised by Haematology for patients on chemotherapy).
Reference ranges:
Updated FLC ranges from 07/05/25
<70 years: Kappa (mg/L): 6.3 - 39.0, Lambda (mg/L): 5.9 – 36.7, K/L ratio: 0.44 – 2.16.
≥70 years: Kappa (mg/L): 7.0 – 55.8, Lambda (mg/L): 6.4 - 48.0, K/L ratio: 0.46 - 2.59.
eGFR 45-59: Kappa (mg/L): 7.8 – 83.6, Lambda (mg/L): 7.3 – 65.1, K/L ratio: 0.46 - 2.62.
eGFR 30-44: Kappa (mg/L): 8.8 – 103.3, Lambda (mg/L): 8.2 – 73.2, K/L ratio: 0.48 – 3.38.
eGFR <30: Kappa (mg/L): 11.7 – 265.1, Lambda (mg/L): 12.6 – 150.9, K/L ratio: 0.54 – 3.30.
Units
mg/L
Turnaround Time
4
days
Department: Biochemistry
Clinical Application
sFLC analysis is used to detect light chain abnormalities when screening patients for myeloma. Subsequent monitoring of sFLC is required in patients diagnosed with myeloma or its precursor condition, Monoclonal Gammopathy of Undetermined Significance (MGUS).
Following a myeloma screen, if a serum paraprotein is detected by protein electrophoresis, the laboratory will add sFLC analysis if not already requested front-line. This aids risk stratification of patients with potential myeloma or MGUS; sFLC replaces the need for urine BJP analysis. Patients should be referred or monitored on the basis of serum electrophoresis and sFLC results, as well as results of other routine Haematology and Biochemistry tests and clinical findings (please see local MGUS guideline below).
When all other clinical and laboratory findings point to MGUS, patients with K:L ratio falling within the extended range of 0.1 – 7.0 may be monitored in the community, initially 6 months after diagnosis, then annually if all clinical and laboratory findings remain stable. Otherwise obtain a Haematology opinion.
Use of the K/L ratio increases the sensitivity of detecting monoclonal sFLC. Raised individual sFLC with normal K/L ratio suggests a polyclonal increase, rather than monoclonal gammopathy; this is a non-specific finding, where sFLC does not require monitoring.
Webpage updated: May 2025.
Links:
» Monoclonal Gammopathy of Undetermined Significance (MGUS) Guideline
