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Serum or plasma mass concentration of free heavy-chain immunoglobulin E (IgE)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of free immunoglobulin E (IgE), a protein involved in allergic reactions, in your blood. Free IgE is distinct from total IgE, which includes bound IgE.

Quick summary

["Assessing free IgE helps evaluate allergic responses and potential immune system activity."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
16735-3
Short code
DHEA p chal SerPl-mCnc
Synonyms
DHEA p chal SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
135
Ref high
980
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82626
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 Free Immunoglobulin E (IgE)?

IgE is a type of antibody that plays a key role in the immune system’s response to allergens. When your body detects allergens (like pollen, dust, or certain foods), IgE helps trigger allergic reactions. Free IgE refers to the portion of IgE that is not bound to other proteins in the bloodstream, which can be measured separately from total IgE levels.

Why Might Your Doctor Order This Test?

Your doctor may request free IgE testing if you have suspected allergies, chronic inflammatory conditions, or if other tests suggest abnormal immune activity. It can also help monitor conditions like allergic asthma, atopic dermatitis, or certain immune disorders.

How Is This Test Performed?

A blood sample is drawn from a vein, usually in your arm. The sample is then processed to separate serum or plasma, where the free IgE concentration is measured using a specialized laboratory technique.

What Does a Result Mean?

Results are not typically provided in absolute numeric ranges, as reference values vary by lab and patient factors. Instead, your doctor will interpret the result in relation to your clinical symptoms and other test results.

Reference range

NCBI: DHEA-S Male 135-980 µg/dL; Female 30-260 µg/dLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free IgE levels

Frequently asked questions

Why do some people have elevated free IgE levels?
Elevated free IgE levels may indicate an overactive allergic response, chronic inflammation, or an underlying immune disorder. However, elevated levels alone do not always mean you have an allergy—your doctor will consider your symptoms and other test results to make a diagnosis.
Can free IgE levels change over time?
Yes, free IgE levels can fluctuate depending on factors like allergens you’re exposed to, underlying health conditions, or treatments (such as allergy immunotherapy). Regular monitoring may be needed for conditions like asthma or severe allergies.
Is this test the same as a total IgE test?
No, free IgE is distinct from total IgE. Total IgE includes both free IgE and IgE that is bound to other proteins, so results may differ depending on the test type. Your doctor will clarify which test was ordered and why.
  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 17, 2026. · Read our editorial policy