Serum Free Light Chain Assay

The serum free light chain (FLC) assay is a laboratory test used to measure the levels of free light chains (FLCs) in the blood. FLCs are proteins produced by plasma cells, which are a type of white blood cell that plays a key role in the immune system.

What are Free Light Chains?

Free light chains are the building blocks of immunoglobulins, also known as antibodies. Immunoglobulins are composed of two heavy chains and two light chains. There are two types of light chains: kappa (κ) and lambda (λ). In a normal individual, the ratio of κ to λ light chains is approximately 2:1.

Why is the Serum Free Light Chain Assay Performed?

The serum FLC assay is primarily used in the diagnosis and monitoring of plasma cell disorders, such as:

• Multiple myeloma
• Monoclonal gammopathy of undetermined significance (MGUS)
• Primary amyloidosis (AL amyloidosis)
• Light chain deposition disease
• Plasma cell leukemia

How is the Test Performed?

The serum FLC assay involves measuring the levels of κ and λ free light chains in the blood using a specialized immunoassay. The test requires a blood sample, which is then sent to a laboratory for analysis.

Interpretation of Results

The results of the serum FLC assay are interpreted based on the ratio of κ to λ light chains and the absolute levels of each type of light chain. An abnormal result may indicate the presence of a plasma cell disorder.

• A high level of one type of light chain (either κ or λ) with a low level of the other type may indicate the presence of a monoclonal gammopathy
• An abnormal κ/λ ratio may also indicate the presence of a plasma cell disorder
• Serial measurements of FLC levels can be used to monitor response to treatment and detect relapse in patients with plasma cell disorders

Clinical Significance

The serum FLC assay has several clinical applications, including:

• Diagnosis of plasma cell disorders
• Monitoring of disease progression and response to treatment
• Prognostication and risk stratification in patients with plasma cell disorders

Limitations and Precautions

The serum FLC assay is not without limitations. False-positive results can occur due to various factors, such as:

• Renal impairment, which can lead to elevated levels of FLCs
• Hemolysis or lipemia, which can interfere with the assay
• Other conditions that can cause an increase in FLC levels, such as chronic inflammation or infection

Therefore, results should be interpreted in conjunction with clinical findings and other laboratory tests to ensure accurate diagnosis and management of plasma cell disorders.

Frequently Asked Questions (FAQs)

What is a Serum free light chain assay?
A blood test measuring free light chains in serum.

Why is the Serum free light chain assay performed?
To diagnose and monitor conditions like multiple myeloma and other plasma cell disorders.

What are free light chains?
Proteins produced by plasma cells, normally part of intact antibodies.

How are results interpreted for this test?
By comparing kappa and lambda free light chain levels and calculating their ratio.

Can the Serum free light chain assay diagnose multiple myeloma?
It can help diagnose, but typically in combination with other tests and clinical findings.

Are there any preparations needed before the test?
Typically no special preparation is required, but this may vary depending on individual circumstances.

What are normal ranges for kappa and lambda free light chains?
Vary by laboratory, generally kappa is around 3.3-19.4 mg/L and lambda around 5.7-26.3 mg/L.

Can elevated free light chain levels be due to non-malignant conditions?
Yes, certain inflammatory and infectious diseases can cause elevations.

How often should the Serum free light chain assay be repeated for monitoring purposes?
Frequency depends on individual patient circumstances and clinical guidelines.

Are there any limitations or potential interferences with this test?
Certain laboratory methods or conditions may interfere with results, affecting accuracy.