Tuberculin (PPD) and the Mantoux Test: TB Infection Screening

Tuberculin (purified protein derivative, PPD) is derived from Mycobacterium tuberculosis. It is used in the Mantoux tuberculin skin test (TST) to detect TB infection.

Procedure

1. Intradermal injection of 0.1 mL tuberculin (5 TU).
2. Read at 48–72 hours: measure induration (hardened raised area) diameter in mm.
3. Interpretation depends on risk factors (e.g., ≥5 mm for HIV/close contacts; ≥10 mm for high-risk groups; ≥15 mm for low risk).

Important Notes

• Positive TST = TB infection (latent or active), not necessarily active disease.
• Further evaluation (chest X-ray, sputum culture) needed to diagnose active TB.
• BCG vaccination can cause false-positive; IGRA blood tests are alternative.

Tine Test (Less Common)

Multiple-prong device applies tuberculin; papule formation at 48–72 hrs indicates reactivity. Less standardized than Mantoux.