The size of induration that signifies a positive result in a 16-year-old client is larger or equal to fifteen (15) mm. A tuberculin test (or Mantoux test) is a medical tool for screening for tuberculosis. The procedure involves the injection of 5 tuberculin units intradermally and the reading of the reaction 48 to 72 hour later. If a person has been exposed to the specific bacteria, the skin will exhibit an immune response. This immune response is in a form of an induration, whose diameter is measured. The diameter in relation to the person's risk factor will determine whether the result will be positive or not.