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  29. Mantoux Test

    The Mantoux test is a skin test used to determine if a person has
    been exposed to tuberculosis (TB) bacteria. It is also known as the **tuberculin test** or **PPD test** (Purified Protein Derivative).

    The Mantoux test involves injecting a small amount of purified
    protein derivative (PPD) into the skin of the forearm.
    This substance is derived from the bacteria that cause TB.

    History

    The Mantoux test was developed in 1905 by French physician Charles Mantoux.
    It became a standard diagnostic tool for tuberculosis
    in many countries until the advent of more accurate and
    reliable tests, such as the interferon-gamma release assay (IGRA) and nucleic
    acid amplification tests.

    Procedure

    The test is typically administered on the inner forearm.
    The healthcare provider uses a needle to inject 2 tuberculin units (TT) of PPD into the superficial
    fascia. A positive reaction usually appears within 2–4 days
    as a small, firm, and red bump that may be accompanied by surrounding erythema.

    Interpretation

    A positive Mantoux test indicates exposure to TB bacteria.
    The size and quality of the skin reaction help determine the likelihood
    of active or latent TB infection. A negative result suggests no exposure, but false negatives can occur in some cases.

    Applications

    The Mantoux test is primarily used for screening individuals who are
    at high risk of TB infection, such as those with a history of close contact with an infected person or immigration from a region with high TB prevalence.

    Limitations

    While the Mantoux test is useful, it has several limitations.
    It can produce false positives (inflammation caused by non-TB pathogens) and false negatives (failure to detect
    true-positive results). Additionally, the test requires careful interpretation by trained personnel.

    Conclusion

    The Mantoux test is a foundational diagnostic tool in tuberculosis control, despite being
    largely surpassed by more modern testing methods. It remains important for disease surveillance and elimination efforts worldwide.

    Contents

    1. **Mantoux Test**
    2. **History**
    3. **Procedure**
    4. **Classification of Tuberculin Reaction**
    5. **False Positive Result**
    6. **False Negative Result**
    7. **BCG Vaccine and the Mantoux Test**
    8. **Anergy Testing**
    9. **Two-Step Testing**
    10. **The Latest Interpretation for Mantoux Test Results**
    11. **Recent Developments**
    12. **Heaf Test**
    13. **See Also**
    14. **References**

    Mantoux Test

    The Mantoux test is a diagnostic tool used to determine if an individual
    has been exposed to Mycobacterium tuberculosis,
    the bacterium that causes tuberculosis (TB). It involves
    injecting a small amount of tuberculin solution into the skin and then observing the resulting reaction.
    This test is a cornerstone in TB diagnosis, providing valuable information for early detection and management of the disease.

    History

    The Mantoux test was developed by French physician Pierre-Marie Gilbert Charpy in 1905.
    Initially called the „Newark test,“ it was later renamed
    after Charles Mantoux, a colleague who improved its methodology.
    Over time, the test has undergone modifications and is now
    a standard diagnostic tool used worldwide, particularly in areas where
    TB is prevalent.

    Procedure

    The Mantoux test is performed by injecting 0.1 mL of purified protein derivative
    (PPD) into the derma of the inner forearm. The site of injection is then read after 48-72 hours.
    A positive reaction is indicated by a firm, raised rash that may become erythematous or necrotic at the edges within 24-72
    hours.

    Classification of Tuberculin Reaction

    The Mantoux test response can be categorized into several types:

    – **Positive**: A clear, raised, and often erythematous
    rash that develops within a few days after injection.
    – **Negative**: No visible reaction at the injection site or a minimal, non-inflammatory response.

    – **Boomerang Reaction**: A delayed response where the rash appears after 72 hours but resolves quickly, mimicking a negative result.

    The size and duration of the rash are important in interpreting
    the results.

    False Positive Result

    A false positive Mantoux test occurs when the skin reacts
    positively even though the individual has not been exposed
    to TB bacteria. This can happen due to:
    – Cross-reactivity with other mycobacterial infections, such as Bovine tuberculosis or Leprae.

    – Use of certain medications (e.g., interferons) that mimic aTB reaction.
    – Rarely, skin inflammation from conditions like eczema or contact dermatitis may cause a false
    positive.

    False Negative Result

    A false negative result occurs when an individual has been exposed to TB but the Mantoux test does not show a positive response.
    This can happen due to:
    – Early infection (before the immune system reacts).

    – Poor technique in administering the test.

    – Pre-existing immune suppression or malnutrition, which weakens
    the body’s response.

    BCG Vaccine and the Mantoux Test

    The BCG (Bacillus Calmette-Guérin) vaccine is widely used to prevent TB, especially in children. However,
    it can cause a false positive Mantoux reaction because the vaccine
    contains antigens similar to those in TB bacteria.
    This means that individuals who have received the BCG vaccine may show a positive Mantoux
    reaction even if they have not been exposed to TB.
    It’s important to interpret such results with caution, as a positive Mantoux test after BCG vaccination does not necessarily indicate active disease.

    Anergy Testing

    Anergy testing is a related procedure used to assess the immune response in individuals with conditions like Human Immunodeficiency Virus (HIV) or cancer.
    It involves injecting a small amount of mumps, yeast, or another antigen and observing
    the lack of reaction (anergy) in individuals with impaired
    immune systems.

    Two-Step Testing

    In high-risk populations, such as those living with HIV/AIDS or in areas with
    high TB prevalence, two-step testing is recommended.
    This involves first performing a Mantoux test and then confirming a positive result with an interferon-gamma release assay (IGRA) or a chest X-ray.

    Two-step testing improves the accuracy of diagnosis, especially in individuals who may
    have a false positive Mantoux reaction due to BCG vaccination.

    The Latest Interpretation for Mantoux Test Results

    Recent studies have clarified that the size and duration of the Mantoux rash are
    critical factors in interpretation. A larger, more persistent rash is more likely to indicate true exposure to TB bacteria, while a
    smaller or fleeting reaction may represent cross-reactivity or a false positive.

    Additionally, guidelines now recommend interpreting Mantoux results within 72 hours of
    injection for accuracy.

    Recent Developments

    Recent advancements in TB diagnostics include the development of new and
    more accurate tests, such as the Xpert MTB/RIF assay, which provides rapid results and can be
    used alongside Mantoux testing. Research is also focusing on improving the accuracy of the Mantoux test in individuals
    vaccinated with BCG and those with pre-existing immune conditions.

    Heaf Test

    The Heaf test is another skin-based diagnostic tool, similar to
    the Mantoux test, but it uses a different antigen (mumps or squalene) and is often used for anergy
    testing in individuals with impaired immune responses. It is
    named after Harald Héaf, a Norwegian physician who contributed significantly to the understanding of TB diagnostics.

    See Also

    – **Tuberculosis Diagnosis**
    – **BCG Vaccine**
    – **Interferon-Gamma Release Assay (IGRA)**
    – **Xpert MTB/RIF Test**

    References

    1. World Health Organization. (2010). Tuberculosis control: Guidelines for national programmes.

    2. American Thoracic Society. (2005). Diagnostic criteria for latent tuberculosis infection.
    3. European Centre for Disease Prevention and Control.
    (2020). Best practices for TB diagnosis in Europe.

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