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Background to Multiple Myeloma and Free Light Chain Testing (FLC Testing)

Multiple Myeloma is the 2nd most common form of haematological malignancy. In Caucasian populations, the incidence is approximately 35 per million, per year and this increases with age. In the UK there are 3,000-3,500 new cases per year, almost 20,000 in the USA and 86,000 worldwide with a median survival or 3-5 years. At any one time, there are estimated to be 500,000 patients with myeloma worldwide.

Multiple Myeloma can present in many different ways, it is typically a disease of the elderly but it can also occur in the young. Bone pain and fractures are characteristic and patients can develop renal failure, acute and chronic infections. Many will require stem cell transplantation and/or intensive chemotherapy. Because of this many clinical specialists, such as haematologists, nephrologists, immunologists, orthopaedic surgeons and chemical pathologists become involved in patient care.

Diagnosis is based on the presence of excess monoclonal plasma cells in the bone marrow, monoclonal proteins in the serum or urine and related organ or tissue impairment such as hypercalcaemia, renal insufficiency, anaemia or bone lesions.

Diagnostic Testing

Historically laboratory protocols for diagnosis of a monoclonal gammopathy have generally been based on the detection of whole immunoglobulin monoclonal protein (M-protein) in serum and urine by serum protein electrophoresis (SPE) and urine protein electrophoresis (UPE). This is followed by immunofixation electrophoresis (IFE) to confirm monoclonality and class of the M-protein. As 15% of all cases of Multiple Myeloma are Light Chain (Bence Jones) Multiple Myeloma with little or no detectable protein in the serum, further analysis has traditionally been required*2. A 24-hour urine sample is concentrated then analysed for the presence of Bence Jones Protein by electrophoresis. Quantification may be performed by densitometric scanning of the gel. In addition to this, these assays were traditionally used to quantify serum free light chains (FLC) – see table 1. However, all of these assays fail to detect FLC in serum at concentrations within the normal range (3-25mg/L).

The first commercially available serum FLC immunoassay became available in 2001 to address this challenge with electrophoretic techniques. These assays had the following features:

  • Highly specific for serum and urine FLC
  • 1000 times more sensitive than serum electrophoretic tests
  • Better precision than electrophoretic tests
  • Provide quantitative results

The availability of the FLC immunoassays led to the measurement of free light chains (FLC) for the diagnosis and monitoring of myeloma and related disorders to be widely published*1-4. As a result of these many years of research, UK, European and International guidelines recommend the measurement of serum FLCs alongside electrophoresis for the diagnosis, prognosis and monitoring of Multiple Myeloma*5-8.

FLC are also recommended as prognostic indicators in Monoclonal Gammopathy of Undetermined Significance (MGUS)*9-10. In MGUS the FLC ratio is helpful in identifying individuals who are at an increased risk of progression to Multiple Myeloma and related disorders.

Monoclonal free light chains are important disease biomarkers in patients with myeloma and related disorders. It is recognised that laboratory algorithms are required that measure both intact immunoglobulins and monoclonal FLC, at diagnosis and when monitoring response to treatment. There has also been over the past few years a focus on the utility of FLC assays to replace urine electrophoresis for monoclonal FLC measurement. Due to the limited sensitivity and practical constraints of urine analysis, a serum-based algorithm of SPE and FLC has been adopted by many laboratories as a first line screen in patients with suspected monoclonal gammopathies.

Table 1 – Comparison of available assays for FLC measurement

ASSAY TYPE Advantages Disadvantages
Total Urine Protein
  • Simple, inexpensive testWidely used
  • Sensitivity inadequate for FLC detection
Serum Protein Electrophoresis (SPE)
  • Simple, manual / semi-automated method
  • Monoclonal bands visualised
  • Quantitative results can be obtained with scanning densitometry
  • Cannot detect FLCs at low concentrations (Insensitive, <500-2000mg/L)
  • Subjective interpretation of results can lead to inconsistency
Urine Protein Electrophoresis (UPE)
  • Simple, manual / semi-automated method
  • Inexpensive & well established
  • Monoclonal bands visualised
  • Quantitative results can be obtained with scanning densitometry
  • Sensitive in concentrated urine (10mg/L)
  • Cumbersome 24-hour urine collection
  • Urine may require concentration
  • False bands from concentrating urine
  • Heavy proteinuria obscures results
  • Subjective interpretation of results can lead to inconsistency
Immunofixation on serum and urine (IFE)
  • Good sensitivity for serum and very sensitive for concentrated urine (5-30mg/L)
  • Well established
  • Serum sensitivity (~150mg/L) inadequate for normal serum FLC levels
  • Non-quantitative
  • Manual / semi-automated technique
Capillary Zone Electrophoresis (CZE)
  • Automated technology
  • Quantitative
  • Less sensitive (~400mg/L) than IFE for serum FLC levels
Total serum / assays
  • Automated immunoassay
  • Specificity inadequate for detecting many patients with light chain monoclonal gammopathies

 

*Please see Resources Page for a full list of references

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