Skip to content

Tuberculosis Mycobacterium Tuberculosis Antibody (IgG) in Blood

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

This test measures antibodies to *Mycobacterium tuberculosis*, the bacterium responsible for tuberculosis (TB). It helps determine if your body has ever been exposed to TB bacteria, even if you don’t currently have active disease.

Quick summary

["This test checks for past exposure to TB, not active infection."]

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

Key facts at a glance

LOINC
45323-3
Short code
M TB tuberc IFN-g Bld Ql
Synonyms
M TB tuberc IFN-g Bld Ql
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What Does This Test Measure?

The test detects IgG antibodies produced by your immune system in response to exposure to *Mycobacterium tuberculosis*. These antibodies are a sign that your body has recognized and fought the bacteria, often years after exposure. This is a marker of past infection, not necessarily current illness.

Why Might I Need This Test?

Healthcare providers may order this test if you have a history of TB exposure, live in a high-risk area, or have symptoms that could suggest TB (like persistent cough, fever, or weight loss). It’s also used in screening for people who may have been vaccinated with BCG (a tuberculosis vaccine used in some countries).

What Does a Positive Result Mean?

A positive result indicates that your immune system has likely encountered TB bacteria before, meaning you may have been exposed. However, this does not confirm active TB disease. Active TB requires additional testing and evaluation by a healthcare provider.

What Does a Negative Result Mean?

A negative result means your body did not produce detectable antibodies to TB bacteria at the time of testing. This could mean you have never been exposed or that the test was taken too soon after exposure for antibodies to develop.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Tuberculosis IgG Antibody (Blood)

Frequently asked questions

How is this test used in clinical practice?
This test is primarily used for screening and surveillance, especially in populations at higher risk of TB exposure. It helps identify individuals who may need further evaluation for latent TB infection (LTBI) or active TB disease. A positive result does not replace other diagnostic tests like a TB skin test or chest X-ray, which are used to assess active infection.
What are the limitations of this test?
This test has some limitations: it may not detect recent or very mild exposures, and it can sometimes produce false positives or negatives. Additionally, people who have been vaccinated with BCG may have false positives due to cross-reacting antibodies. Always discuss results with your healthcare provider.
Can this test be used to diagnose active TB?
No, this test alone cannot diagnose active TB. A positive result suggests past exposure, but active TB requires additional diagnostic tests, such as a TB skin test, chest imaging, or microbiological confirmation (e.g., sputum culture). Always follow up with your healthcare provider for further evaluation.
  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