Final answer:
A positive tuberculin skin test, defined by an induration of 10 millimeters or more, indicates that a patient has been exposed to Mycobacterium tuberculosis and has a cellular immune response to it. The test requires confirmation for diagnosing active tuberculosis.
Step-by-step explanation:
An induration of 10 or more millimeters is considered positive in the tuberculin skin test, also known as the Mantoux test, which is a diagnostic tool for tuberculosis (TB). When tuberculin protein derivative is injected into the skin, a positive reaction is indicated by a raised, hard area called induration, appearing within 48-72 hours. This reaction suggests that the patient has been exposed to Mycobacterium tuberculosis and possesses a cellular immune response against the bacterium.
A positive result, however, does not necessarily mean that a patient currently has active tuberculosis; it could be due to a latent infection or prior exposure. Therefore, further testing may be required to confirm an active infection. Additional tests, such as chest radiography and sputum testing, could be employed alongside the initial skin test to determine the presence of active TB.