Interpretation of tuberculin skin-test results in the diagnosis of tuberculosis in children.

INTRODUCTION The tuberculin skin test is one of the most valuable tests for demonstrating tuberculous infection in both symptomatic and asymptomatic children. However, its application is often undermined by difficulties in interpretation of results arising from its low sensitivity and specificity. OBJECTIVES This review aimed to use the concept of induration distribution analysis to estimate the induration size demarcating positive from negative results in a group of children with suspected tuberculosis, and to compare this cut-off with available guidelines for interpretation of the Mantoux test in the diagnosis of tuberculosis in children. METHODS The results of Mantoux tests of children presenting with suspected tuberculosis over a 12-month period were retrospectively reviewed and plotted on a frequency distribution curve. The distribution was used to define a demarcation between positive and negative reactions. The resultant cut-off was compared with currently published guidelines for interpretation of the Mantoux test. RESULTS Two hundred (200) Mantoux results were analysed out of 202 records reviewed. Induration sizes ranged from 0 to 60 mm, with a mean of 9.4 mm. The induration distribution showed a bimodal pattern, with 103 patients showing no reaction (0 mm), and 96 (48%) patients with an induration size of (3) 5 mm, with the second mode at 15-19 mm. The demarcating antimode was at 5 mm. CONCLUSIONS The induration distribution showed that a cut-off induration size of 5 mm was appropriate for this group of patients. This was in agreement with currently published guidelines for the interpretation of the Mantoux test in the diagnosis of tuberculosis in children.