Skip to content

Immunoglobulin M (IgM) in serum or plasma by mass concentration

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

This test measures the amount of Immunoglobulin M (IgM) antibodies in your blood. IgM is one of the key proteins your immune system uses to fight infections.

Quick summary

["IgM helps identify past infections and immune responses."]

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

Key facts at a glance

LOINC
15185-2
Short code
IgM Fld-mCnc
Synonyms
IgM Fld-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 IgM and why is it measured?

IgM is a type of antibody produced by your immune system during an infection. It appears early in the immune response and can linger longer than other antibodies. This test helps doctors track infections, monitor immune function, or check for conditions like certain autoimmune diseases or chronic infections.

When might you need this test?

Your doctor may order an IgM test if you have symptoms of an infection, if you’ve been exposed to a virus, or if you have a condition that affects your immune system. It can also be used to diagnose or monitor conditions like hepatitis, HIV, Lyme disease, or other infections.

How is the test performed?

A small sample of blood is drawn from a vein in your arm. The blood is then processed to separate the serum or plasma, which is tested for IgM levels using a specialized laboratory technique.

What do the results mean?

Results can vary depending on your health, age, and medical history. Elevated IgM levels may suggest an active infection, immune response, or certain medical conditions. Lower than expected levels might indicate immune system issues or other health concerns.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgM Level

Frequently asked questions

Why might my IgM test be ordered before or after another test?
IgM testing is sometimes used alongside other antibody tests (like IgG) to provide a clearer picture of your immune response. For example, it can help distinguish between recent and past infections or rule out certain conditions like autoimmune diseases.
Can IgM levels change over time?
Yes, IgM levels can fluctuate depending on your health status. After an infection, IgM levels may rise and then fall as your body produces other antibodies (like IgG). Chronic infections or immune disorders may also affect IgM levels over time.
Is there anything I should do to prepare for this test?
No special preparation is usually needed, but avoid alcohol for 24 hours before the test if your doctor recommends it. Let your healthcare provider know about any medications or conditions that might affect results.
  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