I'm sorry to hear this. I have read this from others. They swear they never took anything and yet it shows up mysteriously and they get kicked out of their clinic. Did they tell you specifically what showed up? An opiate blocker, is that an opiate antagonist, actually? Just trying to clarify. The names I have of drugs that are opiate antagonists are methylnaltrexone, nalbuphine, nalmefene, nalorphine, naloxone, naltrexone, and nalorphine. I have read that false positives happen. If you have the money, I'd check with a lawyer. This is ashame you are left without care.
The problem now is the length of time from the first test to the second. Typically most medications taken only show up for a certain. Time frame- depending on the medication.
https://www.drugs.com/mtm/nalmefene.html
The drug that showed up is typically administered in the hospital or by EMS as the result of a suspected overdose.
It is typically administered by vein- or in rare circumstances intrnasally.
At this point there is no way to clear or repeat the test that showed it or validate the follow up test since it would have cleared your system by the time the second test was administered.
Compliance testing and screening are routine in pain management practices- as well as testing for illegal substances , alcohol, or other medications not prescribed to you.
It is EXTREMELY important for any patient to ensure that their urine test sample does not leave your possession until it is labeled and placed in the biohazard bag for processing.
If you took Suboxone or subutex, that would cause a positive result for an opiate blocker.
When testing for compliance or other substances- different opiates break down into specific metabolites in your body- the testing measures those metabolites to ensure you are taking medications exactly as prescribed.
Typically if there is a questionable result- the sample is retested using gas chromatography and mass. Spectrometry to confirm the result.
Metabolites are only present for a set time frame- which would explain why you were negative later.