Skip to content

Immunoglobulin M (IgM) in Serum or Plasma

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 your immune system fight infections, especially those caused by bacteria.

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
25446-6
Short code
IgM Ur Ql IEP
Synonyms
IgM Ur Ql IEP
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
immunoelectrophoresis
CPT
82784
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What Does This Test Measure?

IgM is one of the key proteins your immune system uses to defend against infections. 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 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, such as fever, fatigue, or swollen lymph nodes. It’s also used to diagnose or monitor conditions like hepatitis, certain cancers, or immune disorders. Sometimes, it’s part of a broader evaluation for unexplained illnesses.

What to Expect Before the Test

No special preparation is usually needed. You may have a small needle inserted into a vein (usually in your arm) to draw blood. If you’re nervous, let your healthcare provider know—they can help make it more comfortable.

What to Expect During the Test

The blood sample is sent to a lab for analysis. Results are typically ready within a few days, depending on your lab’s processes. Your doctor will discuss the results with you, explaining what they mean for your health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgM Level

Frequently asked questions

Why is this test important?
IgM levels can indicate recent infections (like bacterial or viral illnesses) or chronic conditions. High levels may suggest an active infection, while persistently elevated levels could point to conditions like autoimmune diseases or long-term immune activation. Low levels might raise concerns about immune system dysfunction.
How does this test compare to other antibody tests?
IgM is often measured alongside other antibodies like IgG and IgA. IgM typically appears first during an infection but decreases over time, while IgG remains longer. Doctors use these tests together to track infection progression or response to treatment.
Can diet or medications affect IgM levels?
Dietary factors or common medications (like some antibiotics or immune-modulating drugs) may indirectly influence immune responses but rarely directly alter IgM levels. Always discuss any medications or supplements with your doctor 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