Mantoux test.

PPD Testing.

Delayed hypersensitivity to PPD( purified protein derivative)

0.1 mL of PPD induces a visible and palpable induration (at least 5 mm in diameter) that peaks in 48 to 72 hours

It does not differentiate between infection and disease

False-negative reactions (or skin test anergy)

viral infections

Malnutrition

Hodgkin's lymphoma

Immunosuppression

overwhelming active tuberculous disease.

False-positive reactions may also result from infection by atypical mycobacteria.

only a small fraction of those who contract an infection develop active disease.