For a brief history of the UDS and a review of the test for benzodiazepines, check out part 1 of our two-part series.
To properly interpret the UDS for opiates.
First, a couple of prerequisites…
1) Opiate vs. Opioid
- These two terms are often used interchangeably and really shouldn’t be.
- Think of it like this: ‘Opioid’ is the broad category name while ‘opiate’ simply refers to the naturally occurring opioids. The term ‘opioid’ encompasses opiates, semi-synthetic, and synthetic agents. The chart below gives a few examples of each.
2) Forgive me in advance for the structures, but I think it’s important to understand why a drug may or may not show up on the UDS. I can’t get rid of the chemist in me…
- The point here isn’t to analyze structures, but simply to see the similarities between morphine, heroin, and oxycodone.
- Oxycodone, a semi-synthetic, is similar to morphine.
- Methadone, a synthetic, has a completely unrelated structure.
- Notice the name of the UDS next time you order one. It is opiates (not opioids).
- The test was designed to look for heroin (technically a semi-synthetic) via its metabolite, 6-monacetyl morphine. It also picks up morphine and codeine.
- The test does not specifically look for oxycodone, hydromorphone, hydrocodone, etc. They can trigger a positive result due to their structural similarities, but not in every case. Therefore, a negative result doesn’t rule out use of these common drugs of abuse.
- Synthetics will never cross-react with the opiate UDS. They are too structurally dissimilar. That’s why we have a separate test for methadone.
A negative result doesn’t rule out opioid ingestion and a positive result only guarantees that heroin, morphine, or codeine is present. Like the benzo screen… not very helpful, in my humble opinion.