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Immunoglobulin M (IgM) in Serum or Plasma by Immunoassay

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

This test measures the amount of Immunoglobulin M (IgM), a type of antibody in your blood. IgM helps fight infections and is often elevated during acute infections or immune responses.

Quick summary

["IgM helps your immune system fight infections and may rise when your body is responding to illness or injury."]

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

Key facts at a glance

LOINC
44875-3
Short code
IgM Ag Skin Ql IF
Synonyms
IgM Ag Skin Ql IF
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
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 Does This Test Measure?

IgM is one of the key proteins in your immune system. It’s produced early in response to infections, often appearing within a few days after exposure. This test helps doctors track immune activity, diagnose certain infections, or evaluate immune system responses.

Why Might You Need This Test?

Your doctor may order an IgM test to check for infections like viral hepatitis, certain bacterial infections, or autoimmune conditions. It can also help monitor immune responses after vaccination or treatment for infections.

When Might You Get Results Back?

Results may take 1–3 business days, depending on your lab. Your doctor will discuss them with you during your follow-up visit.

What Could High or Low IgM Levels Mean?

High IgM levels may indicate an active infection, chronic immune conditions, or exposure to certain toxins. Low IgM levels could suggest immune deficiencies or certain genetic disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

IgM levels are critical for diagnosing acute infections, guiding treatment decisions, and assessing immune function. For example, elevated IgM can signal recent viral exposure (like hepatitis B or C), while persistently low levels may raise concerns about immune system disorders.

Short name

IgM Level

Frequently asked questions

How is this test collected?
A blood sample is drawn from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort afterward.
What should I do before the test?
No special preparation is needed, but avoid heavy meals before the draw if instructed by your doctor.
Can I take this test at home?
No, this test requires a lab sample, so it must be done at a healthcare facility.
  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