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Immunoglobulin M (IgM) in Serum or Plasma (Screening)

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

This test measures the amount of Immunoglobulin M, a type of antibody in your blood. IgM helps your immune system fight infections, especially those caused by bacteria.

Quick summary

["IgM levels can indicate past or current infections and immune responses."]

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

Key facts at a glance

LOINC
18303-8
Short code
IgM Ser Ql IFE
Synonyms
IgM Ser Ql IFE
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
immunofixation
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 IgM Measure?

IgM is one of the key proteins in your immune system that helps your body fight infections. It appears early in the immune response, often within days or weeks after exposure to a pathogen. IgM levels can rise quickly when your body encounters new bacteria or viruses.

Why Might Your Doctor Order This Test?

Your doctor may recommend this test to check for infections like bacterial illnesses (e.g., strep throat, pneumonia), certain viral infections, or to monitor immune responses in conditions like autoimmune diseases or chronic infections.

Common Uses and Conditions

IgM testing is often used to diagnose or monitor conditions such as hepatitis, Lyme disease, syphilis, or other infections. It can also help determine if your immune system is responding to treatments for conditions like lupus or rheumatoid arthritis.

What to Expect Before the Test

No special preparation is needed for this test. You may have a small needle inserted into your arm to draw blood, or a sample may be collected from a vein. If you’re on blood thinners, let your doctor know before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgM Screening

Frequently asked questions

What are the normal IgM levels?
IgM levels vary and aren’t always reported as a single range. Your doctor will interpret the results based on your health history, symptoms, and other tests.
Can IgM levels change with diet or medications?
Diet or over-the-counter medications typically don’t affect IgM levels. However, certain medications (like some immunosuppressants) or chronic illnesses may influence immune responses indirectly.
Does IgM testing hurt?
The blood draw may cause a slight pinch or discomfort, but it usually lasts only a few seconds. Most people feel little to no pain afterward.
  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