Measurement of Tuberculin Skin Test

The measurements made at 72nd hour were significantly higher than those made at 48th hour (median: 8.9 vs 4.5mm, p=0.01). In those subjects with indurations at either or both time points (n=74), the readings taken at 72nd hour were on average 2.1mm (95% confidence interval: 0.3-3.1mm) larger than those at 48th hour. Using an induration of>15mm diameter to define a positive result, there were more positive test results at 72nd hour (24) compared to 48th hour (20).

Conclusion:

We concluded that, in adults, the size of the 5-TU Mantoux reaction is significantly larger at 72nd hour, thus, in clinical practice, tuberculin tests should be read at this time point since negative tests at 48th hour may be false negative.

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