What is the correct dose for a PPD test?

• A. 0.5 mL
• B. 1 mL
• C. 0.1 mL
• D. 2 mL

Answer: (C)

This test relies on injecting a very small amount of tuberculin into the skin to create a precise reaction. The standard amount is 0.1 mL, delivering about 5 tuberculin units, which forms a small wheel in the dermis. This tiny dose is enough to reveal a prior TB sensitization without spreading into deeper tissues or causing excessive skin reactions. If you use a larger volume, it can pool under the skin or travel deeper, making the reading unreliable and increasing the chance of false results or irritation. After 48–72 hours, you measure the induration (not the redness) to determine a positive reaction. So, 0.1 mL is the appropriate dose.