Which nursing assessment indicates a positive reading of a tuberculin (TB) skin test?
A.
1 day after injection with a 10-mm area of redness and swelling
B.
2 days after injection with a 5-mm area of redness and swelling
C.
4 days after injection with a 3-mm area of redness and swelling
D.
5 days after injection with a 2-mm area of redness and swelling
The correct answer and Explanation is :
The correct answer is A. 1 day after injection with a 10-mm area of redness and swelling.
Explanation
A tuberculin skin test (TST), commonly known as the Mantoux test, is used to determine if a person has been infected with the bacterium that causes tuberculosis (TB). The test involves injecting a small amount of purified protein derivative (PPD) intradermally into the forearm. After 48 to 72 hours, the site of injection is examined for induration (swelling) and erythema (redness).
A positive reaction indicates that the immune system has been sensitized to the TB antigens, which can occur due to either a current infection or a previous exposure to the bacteria, whether from active TB or from the Bacillus Calmette-Guérin (BCG) vaccine.
The criteria for a positive TST reading depend on the size of the induration and the individual’s risk factors. A measurement of 10 mm or greater is generally considered positive for individuals at average risk for TB. However, for high-risk populations (like those with weakened immune systems, recent contacts with TB patients, or certain medical conditions), a positive result can be determined with smaller induration sizes.
- Option A: A 10-mm area of induration 1 day after the injection is a clear positive result, as it meets the threshold for those who are at average risk.
- Option B: A 5-mm induration after 2 days may be significant for certain high-risk groups but is not generally considered positive for the average population.
- Option C: A 3-mm area after 4 days does not meet the minimum threshold for a positive result.
- Option D: A 2-mm area after 5 days is also below the positive threshold.
In summary, a positive TST reading of 10 mm within the appropriate time frame signifies a significant reaction and warrants further evaluation for TB infection.