diagnosis for suspected overdose

ED coding newbie...need help with diagnoses:
Child brought to ED by parents for suspected multivitamin ingestion - discovered w/ pill in mouth, not sure of how many ingested (if any). Monitored for iron overdose - 6-hour iron levels were neglible. During monitoring, child showed no ill effects (vomiting, change in behavior, etc) and child was discharged home.

Not sure where to go for a suspected ingestion - use the poisoning codes or maybe V72.85 or V82.5?

Sometimes I think it's harder to code for a non-condition! Thanks for your help, Kim

observation

V71.89 Observation for suspected condition, ruled out.