A paired comparison of tuberculin skin test results in children with clinical manifestations of tuberculosis using 2 TU and 5 TU tuberculins

ABSTRACT

Rationale: A paired comparison of reactivity to purified protein derivative 2 TU PPD RT-23 and 5 TU PPD-S in children with clinical manifestations of tuberculosis was done to assess if 2 TU PPD RT-23 can be used instead of 5 TU PPD-S in routine Mantoux testing in the country. Objective: To determine the correlation of skin test reactivity to 2 TU PPD RT-23 and 5 TU PPD-S. Study Design: Cross Sectional Study. Methods: Two simultaneous skin tests using 2 TU PPD RT-23 and 5 TU PPD-S were performed. Each dose was randomly assigned in a blinded manner to the right or left forearm and read after 72 hours. Correlation between the size of induration obtained with 2 TU PPD RT-23 and with 5 TU PPD-S was done, as well as, correlation between tuberculin reactivity and age, gender, nutritional status, presence of BCG vaccination, exposure, and clinical manifestations. A p-value <0.05 was considered statistically significant. Results: Sixty five patients were included in the study. The overall mean difference in paired reaction sizes for the two doses was-1.02 + 2.8 mm (range of -11 to 3 mm). Using the present guidelines in the country to determine a positive tuberculin skin test, 27 (41.5 %) patients were positive when tested with 2 TU PPD RT-23 and 33 (50.8 %) patients were positive when tested with 5 TU PPD. The mean PPD size with 2 TU was 4.7 mm + 6.1 mm compared to 5.8 mm + 6.1 mm with 5 TU. PPD skin test reactivity with the two reagents was highly correlated (intraclass correlation 0.88; 95% CI 0.83-0.94). There was no significant association between age, gender, nutritional status, presence of BCG vaccination, TB exposure, and clinical manifestations to tuberculin reactivity. Conclusion: Tuberculin skin test reactivity among children, who were with clinical manifestations of tuberculosis and tested with 2 TU PPD RT-23 and 5 TU PPD-S, were found to be comparable. Age, gender, nutritional status, presence of BCG vaccination, TB exposure, and clinical manifestations were not factors influencing the size of the PPD reaction. 2 TU PPD RT-23 can be used instead of 5 TU PPD-S in routine Mantoux testing.