TST results should be read at which time frame after administration?

TST results should be read at which time frame after administration?

• A. Read at 24 hours
• B. Read at 36 hours
• C. Read at 48 hours
• D. Read at 72 hours

Answer: (D)

The Tuberculin Skin Test response is a delayed-type hypersensitivity reaction, so it needs time to develop after injection. T cells at the skin take about 2 to 3 days to mount the induration, with the reaction typically most evident around 48 to 72 hours. Reading earlier (like 24 or 36 hours) can underestimate the size, while waiting beyond 72 hours can lead to fading or confounding changes that make interpretation less reliable. So, the result should be read at about 72 hours after administration to capture the full, stable reaction.

The Tuberculin Skin Test response is a delayed-type hypersensitivity reaction, so it needs time to develop after injection. T cells at the skin take about 2 to 3 days to mount the induration, with the reaction typically most evident around 48 to 72 hours. Reading earlier (like 24 or 36 hours) can underestimate the size, while waiting beyond 72 hours can lead to fading or confounding changes that make interpretation less reliable. So, the result should be read at about 72 hours after administration to capture the full, stable reaction.