Can narcane givin before a uds cause a false positive for opiods?

No: Narcan (naloxone) is an opioid-antagonist. False-positive opiate drug screens have been reported in patients taking Rifampin and quinolones (antibiotics) and in those eating poppy seeds. I don't know of any other causes of a false-positive uds for opiates.

Opioid urine test: Narcane is a true antagonist of the opioids. Although his metabolits are similar in structure with the opioids, the reaction remains negative. No positive urine test.