What does a positive Mantoux (Tuberculin Skin Test) test result indicate and how is it treated?

Understanding and Managing a Positive Mantoux Test

A positive Mantoux tuberculin skin test (TST) indicates infection with Mycobacterium tuberculosis, either as latent tuberculosis infection (LTBI) or potentially active tuberculosis disease, and requires appropriate evaluation and treatment based on clinical context and risk factors.

Interpretation of a Positive Mantoux Test

• A positive Mantoux test represents a delayed-type hypersensitivity reaction to purified protein derivative (PPD), indicating the presence of memory T cells against M. tuberculosis antigens 1, 2

• Interpretation of induration size depends on patient risk factors:

  • ≥5 mm is considered positive in HIV-infected persons, recent contacts of TB cases, persons with fibrotic changes on chest radiograph, and immunosuppressed patients 3, 1
  • ≥10 mm is considered positive in recent immigrants from high-prevalence countries, injection drug users, residents of high-risk settings, and persons with certain medical conditions 3, 1
  • ≥15 mm is considered positive in persons with no known risk factors for TB 3, 1

• False-positive results can occur due to:

  • Previous BCG vaccination (though reactivity typically wanes after 10 years) 1, 4
  • Exposure to nontuberculous mycobacteria 1

• False-negative results can occur in:

  • Immunocompromised patients, especially those with advanced HIV 1
  • Overwhelming TB disease 1
  • Recent live virus vaccination 1

Clinical Evaluation After a Positive Mantoux Test

• A positive Mantoux test alone cannot distinguish between latent TB infection and active TB disease 3, 5

• All patients with a positive Mantoux test should undergo:

  • Thorough symptom assessment (cough, fever, night sweats, weight loss) 1
  • Chest radiography to rule out active pulmonary TB 1
  • Additional testing may include sputum microscopy and culture if symptoms or radiographic findings suggest active disease 1

• Consider interferon-gamma release assays (IGRAs) as complementary tests, especially in BCG-vaccinated individuals, as they have higher specificity 1

• The combination of Mantoux test and IGRA may provide the highest sensitivity (71-83% positive by either test among those who develop TB) 6

Treatment Recommendations

• For active TB disease:

  • Multiple drug therapy is always required; single-drug treatment is inadequate 7
  • Treatment should be supervised by specialists in TB management 1

• For latent TB infection (LTBI):

  • Isoniazid for 9 months is the recommended standard treatment for LTBI in most patients 1, 7
  • Alternative regimens include:
    • Rifampin for 4 months 1
    • Rifampin plus isoniazid for 3 months (3RH) 1
    • Rifampin plus pyrazinamide for 2 months (2RZ) - though this has higher hepatotoxicity 1

• Treatment duration should be extended to 12 months for:

  • HIV-infected persons 7
  • Persons with fibrotic lesions on chest radiograph 7
  • Persons with silicosis 7

Special Considerations

• HIV-infected patients:

  • Have higher risk of progression to active TB 1
  • May have false-negative Mantoux tests due to anergy 1
  • Should receive 12 months of LTBI treatment if infected 7

• Patients starting anti-TNF therapy:

  • Should be screened for TB before starting treatment 1
  • If positive, should complete LTBI treatment before starting anti-TNF therapy when possible 1
  • Have approximately 5-fold increased risk of TB reactivation when on anti-TNF therapy 1

• Recent contacts of infectious TB cases:

  • Should be treated for LTBI regardless of age if Mantoux test is positive (≥5 mm) 7
  • Children and adolescents who are close contacts should receive preventive therapy even if initially tuberculin-negative, with repeat testing after 12 weeks 7

Monitoring During Treatment

• Monitor for hepatotoxicity, especially in:

  • Older patients (>35 years) 1
  • Women (3-4 times higher risk) 1
  • Those with pre-existing liver disease 1
  • Those consuming alcohol 1

• Clinical monitoring for symptoms of hepatitis (nausea, vomiting, abdominal pain, jaundice) should be performed regularly 1

• Adherence to the full course of therapy is crucial for effective prevention of TB disease 1