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How are Tumor Markers Used?

Tumor markers are measurable substances (typically proteins) found in blood samples. Elevated levels may indicate cancer activity, and are interpreted alongside imaging, pathology, and clinical findings rather than used alone for diagnosis.

Common clinical applications include:

  • Monitoring treatment effectiveness
  • Detecting recurrence early
  • Assessing disease prognosis
  • Guiding management decisions

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LifeLabs® Tumor Marker Tests

Serum Free Light Chains (sFLC)

Serum Free Light Chain (sFLC) testing plays a critical role in the diagnosis and monitoring of multiple myeloma and related plasma cell disorders. It detects abnormal monoclonal protein production that may not be identified through traditional serum protein electrophoresis alone. This test measures unbound kappa and lambda immunoglobulin light chains circulating in the blood.

sFLC testing for diagnosis and management of monoclonal gammopathies has been endorsed by both Canadian and International guidelines for more than a decade.

By evaluating both absolute light chain levels and the kappa/lambda ratio, sFLC testing helps clinicians assess disease burden, monitor treatment response, and detect early relapse. It is particularly valuable in light chain myeloma and non-secretory myeloma, where conventional markers may be absent or difficult to interpret.

Early symptoms of multiple myeloma where you may want to consider sFLC testing:

  • Unexplained fatigue
  • Unintentional weight loss
  • Persistent bone pain or fractures
  • Decline in kidney function
  • Hematologic abnormalities
  • Unexplained peripheral neuropathy
  • Heart failure or new arrhythmias
  • Gastrointestinal symptoms
Recognize Myeloma Early

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Serum Free Light Chains (sFLC) Test Details

  • Serum Free Light Chain testing is used in the screening, diagnosis, risk stratification, and ongoing monitoring of plasma cell dyscrasias, including multiple myeloma, smoldering myeloma, monoclonal gammopathy of undetermined significance (MGUS), and related disorders.

    sFLC is used clinically for:

    • Diagnosis of multiple myeloma, primary amyloidosis, MGUS, Waldenström’s macroglobulinemia, and other plasma cell disorders
    • Monitoring minimal residual disease trends
    • Identifying early biochemical relapse
    • Supporting staging systems such as the Revised International Staging System (R-ISS)

    For initial screening, sFLC should be ordered together with other tests such as CBC, WBC differential count, peripheral blood smear, serum calcium with albumin, creatinine clearance (and/or serum creatinine), total serum protein, serum protein electrophoresis (sPEP), serum Immunofixation electrophoresis (sIFE), quantitative immunoglobulins (IgA, IgG, IgM), and general assessments of hepatic and renal parameters.

    Serial measurements allow physicians to track treatment effectiveness and identify changes in clonal activity before clinical symptoms emerge.

  • In plasma cell disorders, malignant plasma cells overproduce either kappa or lambda light chains. An abnormal kappa/lambda ratio suggests monoclonal proliferation. The degree of ratio imbalance often correlates with disease burden.

    sFLC testing is more sensitive than traditional protein electrophoresis in certain subtypes of myeloma. Early detection of rising light chains may allow for timely therapeutic intervention. However, interpretation must consider renal function, as impaired kidney clearance can affect light chain levels.

    In comparison with 24 hour urine protein electrophoresis (uPEP), sFLC shows improved clinical accuracy when combined with sPEP and sIFE. sFLC would also have improved patient compliance compared to the 24hr urine collections which are challenging to do.

  • Testing is performed using an immunoturbidimetric methodology to quantify free (unbound) kappa and lambda light chains in serum. Results are reported as:

    • Kappa free light chain concentration
    • Lambda free light chain concentration
    • Calculated kappa/lambda ratio

    Standardized methodology supports reproducibility and consistency across monitoring intervals.

    Patients are encouraged to choose LifeLabs® consistently as their testing provider for serum free light chains. Measurements with the same assay and same lab ensure ease of comparison and data consistency across time points. If a different lab is used for different timepoints, there is a risk of lower data accuracy and interpretation limitations.

    Results may be available digitally via MCC (My Care Compass) and integrated healthcare provider EMRs.

  • 10 days from sample receipt at LifeLabs® to results reporting.

  • Kappa light chain, Free: 3.3 – 19.4 mg/L

    Lambda Light chain, Free: 5.7 – 26.3 mg/L

    Kappa/Lambda Light chains free with ratio: 0.26 – 1.65

  • The sFLC assay demonstrates high analytical sensitivity and specificity for detecting monoclonal free light chains. When combined with serum protein electrophoresis and immunofixation, diagnostic sensitivity for multiple myeloma exceeds 95%.

    Clinical accuracy is enhanced when results are interpreted longitudinally. Trends over time are more informative than isolated values.

  • sFLC testing requires a physician’s requisition. A standard blood draw can be collected at a LifeLabs® location. Results are reported directly to the ordering healthcare provider about 10 days from sample receipt at LifeLabs® and should be interpreted alongside clinical findings and additional laboratory studies. Please note that this test is not currently ensured by OHIP.

    To receive sFLC, write “free light chains” in the ‘Other Tests’ section of the standard provincial laboratory requisition.