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Tuberculosis Skin Test Reaction Diameter Measurement (Mantoux Method)

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

This test measures the size of your skin reaction after a small amount of purified protein derivative (PPD) is injected under your skin. It helps determine if you’ve been exposed to tuberculosis (TB) bacteria.

Quick summary

["A skin test can help identify past or potential TB exposure by checking your immune response."]

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

Key facts at a glance

LOINC
23539-0
Short code
TB Wheal 3D p Mam Tuberc Diam
Synonyms
TB Wheal 3D p Mam Tuberc Diam
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 This Test Measures

The test involves injecting a small amount of PPD—a protein derived from TB bacteria—into the inner forearm. After 48 to 72 hours, your healthcare provider measures the size of any redness or swelling at the injection site. This diameter is recorded in millimeters.

How the Test Works

If you’ve been exposed to TB bacteria, your immune system may react by causing redness and swelling at the injection site. The size of this reaction helps assess whether you’ve had exposure and whether further testing (like a blood or sputum test) may be needed.

When You Might Need This Test

Your doctor may recommend this test if you have risk factors for TB, such as living or working in a high-risk setting, a recent travel history to areas with higher TB rates, or a weakened immune system. It’s also used in screening programs for people who may not yet show symptoms.

What to Expect Before the Test

No special preparation is needed. Wear comfortable clothing that allows easy access to your arm. Avoid taking antihistamines or steroids 24 hours before the test, as they may affect the results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Tuberculosis Skin Test Diameter

Frequently asked questions

Why did my doctor order this test?
Your doctor may have recommended it to check for TB exposure, especially if you have risk factors like recent travel to high-risk areas, a weakened immune system, or contact with someone who has TB.
What does a positive or negative result mean?
A positive reaction (redness/swelling ≥5 mm) suggests possible TB exposure, but it doesn’t confirm infection. A negative result means no visible reaction, but you may still need further testing if you have risk factors.
How long will I need to wait for results?
Results are typically available within a few days, but your doctor will discuss them with you when they’re ready. Follow-up testing may be needed if your reaction is significant or if you have symptoms of TB.
  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