How is the Mantoux tuberculin skin test performed?

How the Mantoux Test is Performed

The Mantoux test is performed by injecting 0.1 mL of 5 tuberculin units (TU) of purified protein derivative (PPD) intradermally into the volar or dorsal surface of the forearm to produce a visible wheal, then reading the transverse diameter of palpable induration (not erythema) at 48-72 hours. 1, 2

Administration Technique

Injection Procedure

• Inject 0.1 mL of 5 TU PPD intradermally into the volar (inner) or dorsal (outer) surface of the forearm 1, 2
• A visible wheal must form at the injection site—this confirms proper intradermal placement 3
• If significant leakage occurs or the injection is given subcutaneously (no wheal forms), repeat the test immediately at another site 3

Critical Technical Points

The wheal formation is non-negotiable. If you don't see a 5-10 mm raised, blanched wheal immediately after injection, the test was likely placed too deep and must be repeated 3, 4. This is the most common technical error.

Reading the Test

Timing

• Read at 48-72 hours after administration 1, 2
• This timing window is essential for accuracy

Measurement Technique

• Measure only induration (palpable, raised, hardened area), NOT erythema (redness) 1, 2, 3
• Measure the transverse diameter (across the arm, perpendicular to the long axis of the forearm) 2
• Record measurement in millimeters 2
• If erythema >10 mm is present without induration, this suggests the injection was too deep and retesting is indicated 3

Interpretation Thresholds

The test is interpreted using risk-stratified cutoffs 1, 2:

≥5 mm is Positive for:

• HIV-positive persons
• Recent close contacts of TB cases
• Persons with fibrotic changes on chest X-ray consistent with prior TB
• Immunosuppressed patients (organ transplant recipients, those on TNF blockers or high-dose corticosteroids) 1, 2

≥10 mm is Positive for:

• Recent immigrants (within 5 years) from high TB prevalence countries
• Injection drug users
• Residents/employees of high-risk congregate settings (prisons, nursing homes, homeless shelters)
• Healthcare workers and others with occupational TB exposure
• Persons with medical conditions increasing TB risk (diabetes, chronic renal failure, certain malignancies) 1, 2

≥15 mm is Positive for:

• Persons with no known TB risk factors 1, 2

Common Pitfalls to Avoid

Do not use multiple puncture tests (Tine, Heaf) or PPD strengths other than 5 TU—these are insufficiently accurate 2

Prior BCG vaccination is NOT a contraindication to PPD testing, and should not influence your decision to test or your interpretation—the larger the reaction, the more likely it represents true TB infection rather than BCG effect 3, 5

False-negative results occur more frequently in infants, early infection (<6-8 weeks post-exposure), recent viral vaccination, immunosuppression (HIV, overwhelming TB disease), and immunosuppressive medications 1. In these high-risk populations, consider repeat testing or alternative diagnostic approaches even with negative results.