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Serum or Plasma Free Light Chain Ratio (Free Light Chain Ratio, Free LC Ratio)

Published: August 9, 2026Updated: August 17, 2026

This test measures the ratio of free light chains (small protein fragments) in your blood, which can help diagnose conditions affecting plasma cells, such as multiple myeloma or other monoclonal gammopathies.

Quick summary

["This test helps identify abnormal protein production that may signal serious blood disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
90124-9
Short code
RESPONSETEAMLEADERTITLE
Synonyms
—
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0
Ref high
17
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 may also be used to monitor treatment progress for conditions like multiple myeloma or to screen for plasma cell disorders.

What to Expect Before the Test

No special preparation is needed. You may have a blood draw from a vein in your arm. If you’re on blood thinners, let your provider know before the test.

What the Test Results Mean

Results are compared to standard ratios for healthy individuals. Elevated ratios may indicate an overproduction of light chains, which can signal plasma cell disorders. Your provider will discuss findings with you based on your full medical history and symptoms.

Common Conditions Monitored

This test is often used to diagnose or monitor multiple myeloma, plasma cell leukemia, or other monoclonal gammopathies. It can also help track treatment responses or detect early signs of disease progression.

Reference range

NCBI: NSE 0-17 ng/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Light Chain Ratio

Frequently asked questions

What does a high or low free light chain ratio indicate?
A high ratio often suggests an underlying plasma cell disorder, such as multiple myeloma, where too many light chains are produced. A low ratio alone is less common but may indicate other conditions affecting protein metabolism.
How often should this test be repeated?
Your provider will determine the frequency based on your diagnosis, treatment plan, and symptoms. Regular monitoring may be needed if you have a known plasma cell disorder to track disease activity or treatment effectiveness.
Can diet or medications affect this test result?
Dietary changes or most over-the-counter medications typically do not affect free light chain ratios. However, long-term use of certain medications (e.g., chemotherapy) or conditions like kidney disease may influence results. Always discuss your medications with your provider 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 17, 2026. · Read our editorial policy