A Comparative Study of Tuberculin Reactions to 2 TU and 5 TU of Purified Protein Derivative in a Tertiary Care Center

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Introduction: Globally, tuberculosis (TB) is the second leading cause of deaths related to an infectious disease, after HIV. Tuberculin skin testing (TST) which is also called Mantoux test or purified protein derivative (PPD) test remains a useful tool to diagnose TB in children. Current recommendation is to use 2 TU PPD RT23 for all diagnostic purposes. TST or Mantoux test is considered positive if the induration is 10 mm or more. Due to non-availability of 2 TU, unstandardized TST with 5, 10 TU RT23 is in practice which can cause problems in reading of test results. Objectives: The objectives of the study were to compare the tuberculin reaction sizes to 2 TU and 5 TU doses of RT 23 with Tween 80 at 46–48 h and 76–78 h. Methodology: All children who were aged < 18 years and are known case of TB were included in the study. Each child was administered dual intradermal injections with 2 TU and 5 TU doses of tuberculin on the volar aspect of the forearm until a wheal was visible at the injected area. The reactions to both the tests were read at 46–48 h and 70–72 h. Institutional Ethics Committee approval was taken before start of the study. The statistical analysis was performed using SPSS 22 version software. Results A total number of cases included in the study during the study period were 81 cases, out of which 52 (64.19%) were male and 29 (35.8%) were female. Among those 81 cases, the mean reaction to 2 TU at 46–48 h was 12.79 mm and at 76–78 h was 15.33 mm. The mean reaction to 5 TU at 46–48 h was 18.89 mm and at 76–78 h was 22.80 mm. Among the cases, the mean size of induration at 46–48 h was lesser than that of 76–78 h in both 2 TU and 5 TU and it was statistically significant. Reactions to 2 TU and 5 TU PPD can be made comparable using the equation, 5 TU = (2 TU × 0.599) + 11.233 at 46–48 h and 5 TU = (2 TU × 0.074) + 21.66 at 76–78 h. ConclusionThus to conclude, cutaneous hypersensitivity to 2 TU PPD can be made comparison using the equation, 5 TU = (2 TU × 0.