Check the unit on the PPD scale, usually mm or TU.
Identify the induration size, not the redness.
Measure the firm raised area across the forearm.
Use a ruler in millimeters.
Record the exact measurement.
Read the result based on the measured induration only.
0 mm means no induration.
5 mm or more may be positive for high-risk groups.
10 mm or more may be positive for moderate-risk groups.
15 mm or more may be positive for people with no known risk factors.
Follow the clinic’s interpretation criteria for the patient’s risk level.