Mantoux test

There are two major tuberculin skin tests for tuberculosis used in the world.

The Mantoux test is used in the United States and is endorsed by the American Thoracic Society and Centers for Disease Control and Prevention (CDC). Multiple puncture tests such as the Tine test are not recommended.

The Heaf test is used in the United Kingdom and is endorsed by the British Thoracic Society.

Mantoux test

The Mantoux test (or Mantoux screening test, Tuberculin Sensitivity Test, Pirquet test, or PPD test for Purified Protein Derivative) is a diagnostic tool for tuberculosis.

History

Tuberculin is a glycerine extract of the tubercule bacilli. Purified protein derivative (PPD) tuberculin is a precipitate of non-species-specific molecules obtained from filtrates of sterilized, concentrated cultures. It was announced in 1890 by Robert Koch. The test is named after Charles Mantoux, a French physician who developed on the work of Koch and Clemens von Pirquet to create his test in 1907.

Procedure

A standard dose of 10 Tuberculin units (0.2ml) is injected intradermally (into the skin) and read 48 to 72 hours later. A person who has been exposed to the bacteria is expected to mount an immune response in the skin containing the bacterial proteins.

The reaction is read by measuring the diameter of induration (palpable raised hardened area) across the forearm (perpendicular to the long axis) in millimeters. No induration should be recorded as "0 mm". Erythema (redness) should not be measured.

If a person has had a history of a positive tuberculin skin test, another skin test is not needed.

Classification of tuberculin reaction

The results of this test must be interpreted carefully. The person's medical risk factors determine at which millimeter of induration the result is positive (5mm, 10mm, or 15mm). A positive result indicates TB infection.

• 5 mm or more is positive in
  • HIV-positive person
  • Recent contacts of TB case
  • Persons with nodular or fibrotic changes on CXR consistent with old healed TB
  • Patients with organ transplants and other immunosuppressed patients

• 10 mm or more is positive in
  • Recent arrivals (less than 5 years) from high-prevalent countries
  • Injection drug users
  • Residents and employees of high-risk congregate settings (e.g., prisons, nursing homes, hospitals, homeless shelters, etc.)
  • Mycobacteriology lab personnel
  • Persons with clinical conditions that place them at high risk (e.g., diabetes, prolonged corticosteroid therapy, leukemia, end-stage renal disease, chronic malabsorption syndromes, low body weight, etc)
  • Children less than 4 years of age, or children and adolescents exposed to adults in high-risk categories

• 15 mm or more is positive in
  • Persons with no known risk factors for TB
  • (Note: Targeted skin testing programs should only be conducted among high-risk groups)

A tuberculin test conversion is defined as an increase of 10 or more mm within a 2-year period regardless of age.

False negative result

A negative test does not exclude active tuberculosis, especially if the test was done within six to eight weeks of acquiring the infection, if the infection is overwhelming, or if the patient is immunocompromised. Also, very young age less than 6 months old or recent live-virus vaccination (e.g., measles) within 4 to 6 weeks are other factors for possible negative skin test.

False positive result

False positive result may be caused by nontuberculous mycobacteria or recent BCG vaccine

BCG vaccine and the Mantoux test

Tuberculin skin testing is not contraindicated for BCG-vaccinated persons.

Latent TB infection (LTBI) diagnosis and treatment for LTBI is considered for any BCG-vaccinated person whose skin test is 10 mm or greater, if any of these circumstances are present:

• Was contact of another person with infectious TB
• Was born or has resided in a high TB prevalence country
• Is continually exposed to populations where TB prevalence is high.

Anergy testing

Anergy skin testing is no longer routinely recommended.

Two-step testing

Some people with LTBI may have negative skin test reaction when tested years after the infection. Initial skin test may stimulate (boost) the ability to react to tuberculin. Positive reactions to subsequent tests may be misinterpreted as a new infection.

Use two-step testing for initial skin testing of adults who will be retested periodically (e.g., health care workers).

• Return to have first test read 48-72 hours after injection
• If first test is positive, consider the person infected.
• If first test is negative, give second test 1-3 weeks after first injection
• Return to have second test read 48-72 hours after injection
• If second test is positive, consider person infected
• If second test is negative, consider person uninfected

Future developments

In order to improve the Mantoux test, several other tests are being developed. QuantiFERON-TB is a blood test that measures the patient’s immune reactivity to the TB bacteria and is useful for initial and serial testing of persons with an increased risk of latent tuberculosis infection (LTBI). It is not useful in active TB disease. A fact sheet (http://www.cdc.gov/nchstp/tb/pubs/tbfactsheets/250103.htm) from CDC is available.

Heaf Test

The Heaf test is used in the United Kingdom.

The equivalent Mantoux test positive levels done with 10 TU (0.1 ml 100 TU/ml, 1:1000) are

• 0-4 mm induration (Heaf 0-1)
• 5-14 mm induration (Heaf 2)
• >15 mm induration (Heaf 3-4)

See also

• tuberculosis
• Heaf testpl:test Mantoux