Final answer:
Healthy individuals with no TB exposure risk are considered to have a positive Mantoux tuberculin skin test with an induration of 15 mm or greater. Those with HIV or recent TB contact have a lower threshold of 5 mm, while some other high-risk groups have a threshold of 10 mm. False-positive results can occur due to BCG vaccination.
Step-by-step explanation:
A healthy individual with no risk of TB exposure typically exhibits no induration in response to the Mantoux tuberculin skin test. A positive response, indicated by a significant induration, suggests exposure to TB or a cellular immune response. For those with no risk factors, an induration of 15 mm or more is considered positive. Different thresholds apply depending on the individual's risk factors and health status. For instance, individuals with HIV or recent contacts of TB cases are considered positive at an induration of 5 mm or more, and those with certain medical conditions or healthcare workers are considered positive at an induration of 10 mm or more.
An important note is that individuals who have received the BCG vaccine, commonly given in many countries outside the United States, may have a false-positive result due to the immune response developed from the vaccine. Moreover, interpretational criteria for a positive result can be influenced by a range of factors such as the patient's risk of TB infection, medical history, and the local prevalence of TB.