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Monoclonal Protein (M-Protein), Urine

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

A urine test that looks for monoclonal proteins, including free light chains, which may be produced by plasma-cell disorders.

Quick summary

["A detectable urine M-protein can indicate an abnormal plasma-cell protein production process that requires clinical evaluation."]

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

Key facts at a glance

LOINC
67763-3
Short code
HEDIS 2012-13 MPM-A BUN
Synonyms
HEDIS 2012-13 MPM-A BUN
Category
kidney
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
7
Ref high
20
Critical range
— – 100 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84520
SNOMED
2739004
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 this test?

This test examines urine for a monoclonal protein, also called an M-protein. It can detect an abnormal immunoglobulin or its free light chains, sometimes known as Bence Jones protein.

Why might I need this test?

This test may be ordered when evaluating a plasma-cell disorder such as multiple myeloma, monoclonal gammopathy, or related conditions. It may also be used alongside serum protein tests and other laboratory findings.

How is the test performed?

A urine specimen is analyzed in the laboratory, often using protein electrophoresis followed by immunofixation to identify any monoclonal protein. The exact testing method may vary by laboratory.

How do I prepare for the test?

Follow the urine-collection instructions provided by the laboratory or your clinician. Fasting is generally not required, but a timed or 24-hour collection may be requested in some situations.

Reference range

Adult: 7-20 mg/dLN/A

Specimen: serum

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine M-Protein

Frequently asked questions

Does a positive result mean I have multiple myeloma?
No. A positive result shows that a monoclonal protein is present, but other laboratory and clinical findings are needed to determine the cause and make a diagnosis.
What is a urine free light chain?
Free light chains are small pieces of antibodies that can be released in excess by abnormal plasma cells. They may appear in urine and are sometimes called Bence Jones protein.
Can this test be collected at home?
Often, yes, if your clinician provides an appropriate sterile container and collection instructions. Follow the laboratory's directions carefully, especially if a first-morning or timed specimen is requested.
  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