Can a 4-year-old get a Purified Protein Derivative (PPD) test?

Tuberculin Skin Testing in 4-Year-Old Children

Yes, a 4-year-old child can safely receive a PPD (Purified Protein Derivative) skin test for tuberculosis screening. The test is appropriate and recommended for children of all ages when tuberculosis screening is indicated 1, 2.

Administration of PPD in Children

The tuberculin skin test is administered using the Mantoux method:

• 0.1 mL of PPD (5 tuberculin units) is injected intradermally on the volar or dorsal surface of the forearm
• The injection should create a 6-10 mm wheal
• The test must be read 48-72 hours after administration by measuring the induration (hardened area) in millimeters 2

Interpretation in Children

The interpretation of PPD test results in children follows specific guidelines:

• ≥5 mm induration is considered positive in:

  • Children who are close contacts of persons with infectious TB
  • Children with HIV infection
  • Children with immunosuppressive conditions 1, 2

• ≥10 mm induration is considered positive in:

  • Children less than 4 years of age (including the 4-year-old in question)
  • Recent immigrants from high-prevalence countries
  • Children with certain medical conditions (diabetes, chronic renal failure, malnutrition) 1, 3

• ≥15 mm induration is considered positive in:

  • Children with no known risk factors 2

Special Considerations for Young Children

1. Higher risk of dissemination: Children under 4 years of age (including 4-year-olds) are at higher risk for TB dissemination, making early detection particularly important 1

2. Diagnostic challenges: Because it's more difficult to isolate M. tuberculosis from children than adults, the PPD test plays a crucial role in diagnosis 1

3. Interpretation context: For children, the PPD test is often interpreted in conjunction with:

   • History of TB exposure
   • Clinical symptoms
   • Chest radiograph findings 1

4. False negatives: Even without HIV infection, approximately 10% of children with culture-negative TB have a negative TST 1

Precautions and Considerations

• Vaccine timing: If the child has recently received a measles-containing vaccine, the PPD test should either be administered on the same day as the vaccine or delayed by >4 weeks after vaccination to avoid potential suppression of PPD reactivity 1

• BCG vaccination history: If the child has received BCG vaccination, interpretation should consider that the probability of a true TB infection increases with:

  • Larger reaction size
  • Contact with a TB case
  • Origin from a high TB prevalence country
  • Longer time between vaccination and testing 1

• Reading accuracy: The test must be read by trained personnel who can accurately measure induration rather than erythema (redness) 2, 4

Conclusion

The PPD test is a well-established screening tool for tuberculosis that can and should be used in 4-year-old children when indicated. The test is safe, and interpretation guidelines are well-defined for this age group, with particular attention to the 10 mm threshold for positivity in children under 4 years of age.