Tuberculosis Skin Test Interpretation (Mantoux Tuberculin Reaction Diameter)
This test measures the size of a reaction on your skin after you’ve been exposed to a small amount of purified protein derivative (PPD) from tuberculosis bacteria. It helps doctors assess whether you may have been previously exposed to TB.
["This test checks for past or potential tuberculosis exposure by measuring skin reaction size."]
Key facts at a glance
- LOINC
- 32561-3
- Short code
- TB Wheal 1D p Mam Tuberc Diam
- Synonyms
- TB Wheal 1D 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 tiny amount of tuberculin into the inner forearm. After 48 to 72 hours, a doctor or nurse measures the size of any raised, red bump (induration) or swelling at the injection site. The diameter of this reaction is recorded in millimeters. This measurement indicates the body’s immune response to tuberculosis exposure.
How the Test Works
The tuberculin used in this test is derived from proteins found in Mycobacterium tuberculosis, the bacterium responsible for tuberculosis. If your body has been exposed to TB before, your immune system will react by producing certain white blood cells that cause a localized skin reaction. The size of this reaction helps determine the likelihood of prior exposure.
Why It’s Done
Doctors may order this test to screen for tuberculosis exposure, especially in high-risk groups like those with weakened immune systems, recent travelers from areas with higher TB rates, or individuals living in close contact with someone diagnosed with TB.
What to Expect Before the Test
No special preparation is needed. Wear comfortable clothing that allows easy access to your arm. Avoid applying lotions, creams, or perfumes to the arm where the test will be done, as they may interfere with the test results.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
A positive reaction (induration ≥5 mm in most cases, or ≥10 mm in high-risk individuals) suggests past exposure to TB. However, a positive result does not always mean you have active TB; it may indicate immunity. A negative reaction means no detectable immune response to TB, which may require further testing if TB exposure is suspected.
Short name
TST Diameter
Frequently asked questions
How long does the test take?
What does a positive result mean?
Can I get the test results over the phone?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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