Narcan Causing False Negative on Blood Test?

Background: My nephew has just recently entered a 30 day inpatient program after an OD and 3 days in a detox program. This is not his first time in rehab and we want him to go into a long term half way house out of state after his 30 day program.

Question: We believe that the OD was caused from heroin b/c of his history with the drug. He is trying to manipulate his mother into not going into long term care. He is saying it wasn’t an OD from heroin and is in denial about his problem. The blood tests that were taken at the hospital can’t confirm that it was heroin he used. I’m wondering if the Narcan they gave him could cause a false negative on his blood work.

Anybody in the medical world that could provide some insight? We are praying once out of state and in long term care it will give him a chance to look at his life from a sober point of view and make the necessary changes. He is trying to guilt trip his mom and I want to show her the tests can be wrong