Interpretation of tuberculin skin test in bacillus calmette–guerin-vaccinated children

Abstract

Objective: The objective was to determine the sensitivity and specificity of tuberculin skin test (TST) in Bacillus Calmette–Guerin (BCG)-vaccinated children for diagnosis of tuberculosis (TB). Materials and Methods: This observational study was conducted at a single tertiary care center over a period of 32 months from March 2012 to November 2014. All children up to 15 years of age who had received BCG at birth, suspected of TB, and referred to pediatric TB clinic were enrolled in the study. All patients were given TST by 5 Tuberculin Unit Purified Protein Derivative-Standard. The diagnosis of TB was based on either clinical, histopathological, or bacteriological grounds. Results: Out of 371 patients, 341 (91.91%) had TB. TST was positive in 227 (61.2%) and negative in 144 (38.8%) patients. The sensitivity of TST to detect active TB was 62.8% and specificity was 56.7%. TST cutoff as ≥15 mm increased specificity of TST to 73.3%, but sensitivity decreased to 25.8%. Age, gender, and contact with TB patients did not affect TST results. Conclusion: The accuracy of TST for the diagnosis of TB is low with low sensitivity and specificity. By increasing the cutoff for positive TST to >15 mm, the number of false-positive TST can be reduced.