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Serum or Plasma Free Light Chain Kappa to Lambda Ratio (Free Light Chain Ratio)

Published: August 9, 2026Updated: August 16, 2026

This test measures the ratio of free kappa and lambda light chains in your blood, which helps assess conditions affecting plasma cells, such as multiple myeloma or other monoclonal gammopathies.

Quick summary

["This test helps diagnose and monitor blood disorders linked to abnormal protein production."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
39912-1
Short code
NM Hrt FP+WM+VV+EF W RNC IV
Synonyms
NM Hrt FP+WM+VV+EF W RNC IV
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
nm
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What Is a Free Light Chain Ratio Test Used For?

A free light chain ratio test is primarily used to detect and monitor conditions where plasma cells produce an excess of either kappa or lambda light chains, such as multiple myeloma, lymphoma, or other monoclonal gammopathies. It can also help evaluate kidney function indirectly, as light chains can affect kidney filtration.

How Is the Test Performed?

You’ll provide a blood sample (serum or plasma) during a routine venipuncture. The lab processes the sample to separate and measure the free kappa and lambda light chains using immunoassay techniques.

Preparation and Sample Collection

No special preparation is needed. The test is typically done as part of a routine blood draw. If you’re on blood-thinning medication, inform your healthcare provider before the test.

What Are the Results Typically Used For?

Results are used to calculate the kappa to lambda ratio, which helps determine if light chain production is abnormal. Elevated ratios may indicate conditions like multiple myeloma, while normal ratios suggest no significant monoclonal gammopathy.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Light Chain Ratio

Frequently asked questions

Why might my doctor order this test?
Your doctor may order this test if you have symptoms of a blood disorder (e.g., fatigue, bone pain), if you’ve been diagnosed with a plasma cell disorder, or if you have unexplained kidney issues. It’s also used in monitoring treatment progress for conditions like multiple myeloma.
What do abnormal results mean?
An abnormal ratio (typically elevated) suggests an excess of one type of light chain, which can indicate conditions like multiple myeloma or other plasma cell disorders. Your doctor will discuss the results in detail and may recommend further testing or treatment.
How often is this test repeated?
This test may be repeated periodically if you’re being treated for a condition affecting light chain production, such as multiple myeloma. Follow your doctor’s instructions for follow-up testing.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy