Final answer:
The two-step Mantoux test for TB screening involves administering a second skin test 1-3 weeks after the initial one to ensure a more accurate detection of TB exposure. It consists of injecting tuberculin into the skin and checking for a reaction after 48-72 hours. False positives can occur with prior BCG vaccination, and positive results warrant additional testing.
Step-by-step explanation:
A two-step Mantoux test for tuberculosis (TB) screening involves an initial tuberculin skin test, followed by a second test administered 1-3 weeks later if the first test is negative. This process is necessary because some individuals with previous TB exposure might not react to a single test if their immune system's response has waned over time. The second test can boost their immune response, causing a delayed-type hypersensitivity reaction on the second test. The Mantoux test involves injecting purified tuberculin material into the skin and checking for a reaction, such as redness, swelling, or hardness (induration), 48-72 hours later as evidence of exposure to TB. However, a positive test does not necessarily signify active infection, as it could indicate a prior resolved TB case or latent TB exposure.
It's important to note that a Mantoux test can have a Type I error, with a 10 percent probability of indicating TB when it is not present, or a Type II error, with a 20 percent probability of failing to detect TB when it is indeed present. The BCG vaccine, used in many parts of the world, can cause a false-positive Mantoux test, reducing the test's usefulness in those populations. A positive result from the Mantoux test usually leads to further testing with chest radiographs to confirm TB exposure.