Youngest Age for PPD Testing
PPD (tuberculin skin testing) can be performed starting at 3 months of age in high-risk populations, particularly HIV-infected children, with annual testing recommended thereafter. 1
Age-Based Recommendations for PPD Testing
High-Risk Pediatric Populations
For HIV-infected children, annual Mantoux tuberculin skin testing should begin at age 3-12 months using intradermally injected 5 TU purified protein derivative (PPD). 1
Children younger than 4 years of age are considered at increased risk for tuberculosis and warrant PPD testing with a positive cutoff of ≥10 mm induration. 1, 2
All infants and children younger than 4 years with ≥10 mm skin test induration are classified as recent converters and candidates for preventive therapy. 2
Special Circumstances in Newborns
For newborns exposed to mothers with infectious tuberculosis, tuberculin skin testing should be performed at 3 months after starting isoniazid prophylaxis, not at birth. 3
Tuberculin-negative (<5 mm) children and adolescents who have been close contacts of infectious persons within the past 3 months should receive preventive therapy until a repeat tuberculin skin test is done 12 weeks after contact with the infectious source. 2
Critical Clinical Considerations
Why Testing Below 3 Months Is Problematic
False-negative reactions occur more frequently in infants and young children, particularly early (<6-8 weeks) after infection, due to immature cellular immune responses. 1
Children aged <2 years or those with HIV infection are more likely to have negative skin tests even when infected with tuberculosis. 1
Interpretation in Young Children
Among children and adults with HIV infection, >5 mm of induration is considered a positive (diagnostic) reaction. 1
For children younger than 4 years who are contacts of TB cases or have other risk factors, >10 mm induration is considered positive. 1
Common Pitfalls to Avoid
Do not use multiple puncture TB skin tests (e.g., Tine tests) in any age group—only the Mantoux method with intradermal injection is recommended. 1
Do not delay PPD testing in exposed infants while waiting for symptoms to develop—the 3-month checkpoint after exposure is critical for detecting infection. 3
Do not give BCG vaccination before completing the 3-month assessment in exposed infants, as this can complicate interpretation of subsequent TST results. 3
Do not assume a negative PPD rules out tuberculosis disease in young children, as approximately 10% of children without HIV infection but with culture-positive TB disease do not react initially to TST. 1
Practical Algorithm for Young Children
For routine screening in high-risk children:
- Begin annual PPD testing at 3-12 months of age in HIV-infected children 1
- Test children <4 years with known TB exposure immediately, regardless of age 1, 2
For newborns with maternal TB exposure: