Does the Mantoux (tuberculin skin test) help in diagnosing tuberculosis?

Does the Mantoux Test Help in Diagnosing Tuberculosis?

Yes, the Mantoux tuberculin skin test (TST) is a valuable and established diagnostic tool for identifying tuberculosis infection, though it cannot distinguish between latent TB infection (LTBI) and active TB disease, and has important limitations in sensitivity and specificity that must be understood for proper interpretation. 1

Primary Diagnostic Utility

The Mantoux test serves two critical functions in TB diagnosis:

• Identifies TB infection (not disease): The TST detects cell-mediated immune response to Mycobacterium tuberculosis antigens, indicating that a person has been infected with TB bacteria 1, 2
• High sensitivity in immunocompetent individuals: The test demonstrates 95-98% sensitivity in clinically well persons with previously treated tuberculosis 1, 3
• Requires additional evaluation: All positive TST results must be followed by symptom assessment and chest radiography to distinguish between latent infection and active disease 2, 4

Proper Administration and Interpretation

Testing Technique

• Standard method: Intradermal injection of 0.1 mL of purified protein derivative (PPD, 5 TU) into the volar forearm surface using the Mantoux method 1, 4
• Reading timing: Measure transverse diameter of palpable induration (not erythema) at 48-72 hours 1, 4
• Measurement specificity: Only the hard, raised, palpable swelling counts—redness alone should not be measured 4

Risk-Stratified Interpretation Thresholds

The American Thoracic Society and CDC recommend three interpretation cutoffs based on patient risk 1, 5, 2:

• ≥5 mm positive for:

  • HIV-infected persons 1, 4
  • Recent close contacts of TB cases 1, 2
  • Persons with fibrotic chest radiograph changes 2, 4
  • Immunosuppressed patients (organ transplant recipients, TNF-blocker therapy, high-dose corticosteroids) 1, 2

• ≥10 mm positive for:

  • Recent immigrants from high TB prevalence countries 1, 5, 2
  • Injection drug users 2, 4
  • Residents/employees of high-risk congregate settings (prisons, homeless shelters, healthcare facilities) 1, 2
  • Persons with medical conditions increasing TB risk 1, 2

• ≥15 mm positive for:

  • Persons with no known TB risk factors 1, 5, 2

Critical Limitations and False Results

False-Negative Reactions Occur In:

• Immunocompromised states: HIV infection causes anergy even in TB-infected persons, reducing test sensitivity 1
• Early infection: TST may be negative in the first 6-8 weeks after TB exposure 1
• Severe/disseminated TB: Up to 50% of patients with miliary TB or TB meningitis have initially negative TST 1
• Young children: Infants and children under 2 years have higher rates of false-negative results 1
• Recent viral infections or vaccinations: Can temporarily suppress TST reactivity 1
• Overwhelming illness: Critically ill patients may not mount adequate immune response 1

Specificity Issues:

• BCG vaccination: Prior BCG causes positive TST reactions, though the American Thoracic Society and CDC recommend interpreting positive results as true TB infection in BCG-vaccinated individuals, especially from high-prevalence countries 5
• Cross-reactivity: Environmental mycobacteria can cause false-positive reactions 6
• BCG effect wanes: Tuberculin sensitivity from BCG typically decreases over time and is unlikely to persist beyond 10 years 5, 4

Special Population Considerations

HIV-Infected Patients

• Lower threshold required: Use ≥5 mm cutoff due to impaired immune response 1, 4
• Test all HIV patients: TST should be performed as soon as possible after HIV diagnosis 1
• Repeat testing after exposure: All HIV-infected persons should receive TST within 7 days of TB exposure regardless of previous results 1
• Anergy testing no longer recommended: CDC states anergy testing is not useful for routine TB screening decisions in HIV populations 1

Children

• Annual testing recommended: HIV-infected children should receive annual Mantoux testing beginning at 3-12 months of age 1
• Lower sensitivity: Approximately 10% of children without HIV but with culture-positive TB have negative TST initially 1
• Diagnosis relies on epidemiologic links: Because children rarely produce sputum and have low bacterial loads, diagnosis often requires linking the child to an adult with confirmed TB plus positive TST and abnormal radiograph 1, 6

When to Use Alternative Testing

For patients ≥5 years old with prior BCG vaccination, interferon-gamma release assays (IGRAs) are preferred over TST due to higher specificity and no BCG interference 5. IGRAs also show promise as potential replacements for Mantoux testing in various populations, with comparable sensitivity (77% in active TB) and better specificity 7, 8.

Common Pitfalls to Avoid

• Do not rely on TST alone in children: Negative TST does not exclude TB disease, especially in HIV-infected or very young children 1
• Do not ignore positive TST in BCG-vaccinated persons: Treat as true TB infection, particularly in high-risk individuals 5, 4
• Do not use multiple puncture tests (Tine): Only the Mantoux intradermal method is recommended 1
• Do not record results as "negative": Document actual induration measurement in millimeters, including "0 mm" if no induration present 4
• Do not measure erythema: Only palpable induration counts for interpretation 4