Burnt and Killer are right on point. There is no upper level limit to creatinine clearance and you don't tell people at the collection site what prescription meds you are on. If you fail for a control prescription med, it's the MRO's job to verify it and keep it as confidential as possible. I forgot when the MRO can and can't disclose this info but basically they decided about 10 years ago it was pointless to tell the collector since the MRO would be the one verifying it.