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Serum or Plasma Free Light Chain Kappa (FLC) Ratio

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

This test measures the ratio of free kappa and lambda light chains in your blood, which can help diagnose conditions like multiple myeloma or other blood disorders.

Quick summary

["Light chain ratios help identify abnormal protein production in your immune system."]

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

Key facts at a glance

LOINC
18048-9
Short code
LV EF US.2D.MOD-SP
Synonyms
LV EF US.2D.MOD-SP
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-d-mod-single-plane
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

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms like unexplained fatigue, frequent infections, bone pain, or kidney problems. It’s also used to monitor conditions like multiple myeloma, lymphoma, or other blood disorders affecting protein production.

What to Expect Before the Test

No special preparation is needed. You may fast before the test, but your provider will let you know if fasting is required. Bring any medications you’re taking, as some may affect results.

How the Test Works

A blood sample is drawn from a vein in your arm. The sample is then analyzed to measure the levels of free kappa and lambda light chains separately and their ratio.

Possible Results and Interpretation

Abnormal ratios (either high or low) may indicate conditions like multiple myeloma, where the body overproduces abnormal proteins. Your provider will discuss results with you based on your symptoms and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Light Chain Disorders

Short name

Free Light Chain Ratio

Frequently asked questions

What causes abnormal light chain ratios?
Abnormal light chain ratios often result from conditions like multiple myeloma, where plasma cells produce too many abnormal light chains. Other causes may include certain lymphomas, amyloidosis, or chronic kidney disease.
How often should this test be repeated?
If you have a known condition affecting light chains (e.g., multiple myeloma), your provider may order this test regularly to monitor disease progression or response to treatment. Follow-up timing depends on your specific diagnosis and treatment plan.
Can diet or medications affect this test?
Some medications (e.g., certain chemotherapy drugs) or kidney issues may influence light chain levels. Always inform your provider about all medications, supplements, or recent illnesses before 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