After administering the annual Mantoux tuberculin skin test to employees, the nurse instructs the staff to return within how many hours after administration to have the results determined?

Number 3 is correct.

The Center for Disease Control recommends the skin test be read 48 – 72 hours after administration. A test is considered positive if an induration of 5 – 15 millimeters is observed at the injection site. Results read after 72 hours are not accurate and another skin test needs to be conducted.