Final answer:
A tuberculin skin test with an induration of 15mm or greater indicates a positive result for tuberculosis infection.
Step-by-step explanation:
A tuberculin skin test shows an induration of 15mm or greater. This result indicates that the test is positive for tuberculosis infection. When the test shows an induration of this size or larger, it suggests that the patient has been exposed to the bacteria and has developed a cellular immune response to it.