Tuberculin reactivity in adult BCG-vaccinated subjects: a cross-sectional study

Int J Tuberc Lung Dis. 2003 Apr;7(4):320-6.


Introduction: Interpretation of the tuberculin skin test (TST) may be complicated by prior bacille Calmette-Guérin (BCG) vaccination. The skin reaction to the vaccination interferes with the management of individuals who may be infected with Mycobacterium tuberculosis.

Objective: To discriminate between TST reactions due to infection and those due to vaccination in subjects with unknown BCG status.

Methods: Among 60200 subjects tested with 5TU PPD for screening purposes, 4987 contacts of infectious TB cases (Group A), 4962 BCG-vaccinated subjects (Group B) and 5000 subjects from the general population (Group C) were sampled. The frequencies of TST cut-off diameters were calculated for the three groups using a logistic regression model. The frequency of positive subjects in each group and the sensitivity, specificity and predictive values were also computed by means of these cut-offs.

Results: The risk of being a contact versus BCG-vaccinated increases 2.43-fold with every mm of TST diameter. The 11 mm cut-off point seems to be the best discriminating value.

Conclusions: Using the traditional 10 mm cut-off, we can consider all vaccinated subjects with a positive TST to be infected. The TST remains a valuable tool for the evaluation of household contacts and suspected cases of tuberculosis in BCG-vaccinated subjects and in populations with high vaccination coverage.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • BCG Vaccine / administration & dosage*
  • Cross-Sectional Studies
  • False Negative Reactions
  • False Positive Reactions
  • Female
  • Humans
  • Male
  • Predictive Value of Tests
  • Probability
  • Retrospective Studies
  • Risk Assessment
  • Sensitivity and Specificity
  • Tuberculin Test / methods*
  • Tuberculosis, Pulmonary / diagnosis*
  • Tuberculosis, Pulmonary / immunology
  • Tuberculosis, Pulmonary / prevention & control*
  • Vaccination / methods


  • BCG Vaccine