Serum Free Light Chains Test: Kappa/Lambda Ratio & Results

Overview

The Serum Free Light Chains (sFLC) Test is an important blood test that measures the levels of free kappa (κ) and free lambda (λ) light chains circulating in the bloodstream.

Light chains are small protein components that form part of antibodies, which are produced by plasma cells in the bone marrow. Normally, these light chains attach to heavy chains to create a complete antibody. However, a small amount of “free” light chains always circulates in the blood.

Abnormally high or abnormal ratios of these free light chains often indicate problems with plasma cells, such as:

• Multiple Myeloma
• MGUS (Monoclonal Gammopathy of Undetermined Significance)
• Light Chain Amyloidosis
• Waldenström’s Macroglobulinemia
• Chronic Kidney Disease

The test is vital for early diagnosis, treatment planning, and monitoring these conditions.

Where Are Free Light Chains Produced in the Body?

Free light chains (kappa and lambda) are produced by plasma cells, a type of white blood cell located inside the bone marrow. Plasma cells are responsible for making antibodies that help protect the body from infections.

When the immune system is functioning normally:

• Plasma cells produce antibodies
• Each antibody has 2 heavy chains and 2 light chains
• A small portion of unused light chains enter the bloodstream as “free” light chains

If plasma cells become abnormal or cancerous, they may produce excessive amounts of one type of light chain, causing disease.

Main Functions and Importance of Light Chains

Although free light chains themselves don’t perform direct immune functions, they are essential parts of antibodies. Their presence is widely used in diagnostics.

1. Essential Component of Antibodies

Light chains combine with heavy chains to form immunoglobulins (antibodies), which defend the body against infections.

2. Support Immune System Defense

Healthy antibody production requires balanced levels of kappa and lambda chains.

3. Diagnostic Marker for Plasma Cell Disorders

Measurement of kappa, lambda, and their ratio (κ/λ ratio) helps detect:

• Multiple myeloma
• MGUS
• Amyloidosis
• Other monoclonal gammopathies

4. Helps Determine Monoclonal or Polyclonal Activity

The κ/λ ratio is one of the most important indicators.

• If the ratio is high, it suggests excess kappa chain production (kappa-type myeloma).
• If the ratio is low, it suggests excess lambda chain production (lambda-type myeloma).

Causes of Low / Negative Free Light Chain Levels

Low serum free light chain levels generally occur when the bone marrow is unable to produce adequate antibodies.

1. Reduced Plasma Cell Activity

This may happen in:

• Certain viral infections
• Immunodeficiency disorders
• Nutritional deficiencies

2. Bone Marrow Suppression

Conditions that reduce bone marrow output include:

• Aplastic anemia
• Chemotherapy or radiation therapy
• Certain autoimmune diseases

3. Immunodeficiency Disorders

These can cause persistently low kappa and lambda levels.

Symptoms of Low / Negative Free Light Chains

Low levels reduce the body’s ability to fight infections.

Common symptoms include:

• Frequent infections
• Weak immune response
• Fatigue
• Slow wound healing
• General weakness

These symptoms reflect poor antibody production.

Causes of High / Positive Free Light Chain Levels

High or abnormal levels often indicate monoclonal plasma cell disorders or conditions where light chains cannot be properly removed from the body.

1. Multiple Myeloma

Cancer of plasma cells, leading to excessive production of one type of light chain.

2. Light Chain Amyloidosis

Abnormal light chains deposit in organs such as kidneys, heart, and liver.

3. MGUS (Monoclonal Gammopathy of Undetermined Significance)

A precancerous condition that may progress to multiple myeloma.

4. Waldenström’s Macroglobulinemia

A type of non-Hodgkin lymphoma involving abnormal antibody production.

5. Chronic Kidney Disease

The kidneys normally filter light chains. When kidney function decreases, free light chain levels increase in the bloodstream.

Symptoms of High / Positive Levels

Depending on the underlying disorder, symptoms may include:

1. Bone Pain

A key symptom in multiple myeloma, especially in the spine, ribs, or hips.

2. Fatigue and Weakness

Often caused by anemia or kidney involvement.

3. Kidney Problems

• Protein in urine (proteinuria)
• Swelling in legs and ankles
• Reduced urine output

4. Nerve Symptoms (Neuropathy)

• Numbness
• Tingling
• Burning sensation

5. Unexplained Weight Loss

Common in cancerous or chronic systemic conditions.

6. Recurrent Infections

Due to poor antibody function.

Reference Ranges

These values may vary slightly based on the laboratory.

An abnormal ratio is the most important indicator of monoclonal plasma cell disorders.

Sample Type

The test requires a:

• Blood sample (serum)
  No special tube is needed beyond standard serum collection.

Test Preparation

• No fasting required
• Continue normal diet and medicines unless doctor advises otherwise
• Inform the doctor if you are on chemotherapy or have kidney problems, as this may affect results

When to Consult a Doctor

Seek medical evaluation if you experience:

• Persistent bone pain
• Frequent infections
• Fatigue or unexplained weakness
• Swelling in legs or reduced urination
• Unexplained weight loss
• Tingling or numbness
• Family or personal history of multiple myeloma or MGUS

Early testing helps in early diagnosis and better outcomes.

Important Word Explanations

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