Earlier Mantoux test was considered as the specific diagnostic test for tuberculosis. However, the co-existence of another disease, age, and immunological status has made the result controversial.
Five units of tuberculin (TU- 0. 1 ML) is injected into the left forearm under the skin, and the result is interpreted as a period 48 to 72 hours. If the injection is correctly done there should be a pale red elevation of 6 to 10 millimeter in diameter. The presence or absence of induration is the basis to determine whether the test is positive or negative. The induration should be determined by inspection in side view and palpation.
The test determines the hypersensitivity to tuberculin. The size of induration has nothing to do with the current active tuberculosis. But the positive reaction can be interpreted as the future risk of developing TB.
X The test is read as positive if the induration is 5 mm or above.
X False-positive reaction is seen in cases of previous vaccination with BCG.
X False-negative reaction is seen in viral infections such as measles and chicken pox.
X Recent live vaccination, e.g.; measles
X Very old as well as recent TB infection
