How long after placement is a TB skin test read?

How long after placement is a TB skin test read?

• A. 24-48 hours
• B. 48-72 hours
• C. 72-96 hours
• D. 1 week

Answer: (B)

The reading window for a TB skin test is 48 to 72 hours after placement because the induration from a delayed-type hypersensitivity reaction to tuberculin develops and becomes measurable within about two to three days. Reading too soon, around 24–48 hours, may miss the full induration and underestimate the reaction. Waiting longer than about 72 hours can allow the reaction to fade or change, making the result less reliable. When you read it, you measure the size of the induration (not the redness) in millimeters.

The reading window for a TB skin test is 48 to 72 hours after placement because the induration from a delayed-type hypersensitivity reaction to tuberculin develops and becomes measurable within about two to three days. Reading too soon, around 24–48 hours, may miss the full induration and underestimate the reaction. Waiting longer than about 72 hours can allow the reaction to fade or change, making the result less reliable. When you read it, you measure the size of the induration (not the redness) in millimeters.