Check the induration, not the redness

Measure the raised, firm swelling in millimeters

Read the test 48 to 72 hours after placement

Use the correct risk-based cutoff for positivity

5 mm positive for highest-risk groups

10 mm positive for moderate-risk groups

15 mm positive for people with no known risk factors

Record the exact millimeter measurement

Document the date and time of reading

If no induration is present, record 0 mm

If the reading is late, do not interpret it as valid

Have a trained clinician interpret the result