I work for a relatively small facility that incorporates computerized random drug testing on a programed percentage of nurses in each unit every month, often several times monthly, and the testing is spread out inconsistently during the month so that no one can predict when it's coming. Thus, the fact that one was already been tested during a given month does not mean that s/he won't be tested again during that same month. If the controlled substance count is off, everyone that worked in that unit during that shift and had access to the Pyxis is tested. If there is an on-the-job injury or a patient incident of any kind, the nurse involved is tested. If a nurse behaves in any manner that "sends up a flag" (obvious drowsiness on the job, habitual or frequent absences, etc.), s/he is probably going to be drug screened. And yes, employees in other departments are randomly tested as well.