Can a Patient on Norco Test Positive for Oxycodone on UDS?
No, a patient taking only Norco (hydrocodone) should not test positive for oxycodone on a properly performed urine drug screen, as hydrocodone and oxycodone are distinct molecules that do not cross-react on confirmatory testing. 1
Understanding the Testing Limitations
- Standard opiate immunoassays are designed to detect morphine and codeine, creating a critical gap in detecting synthetic opioids like both hydrocodone and oxycodone. 1
- Standard immunoassay screens often fail to detect hydrocodone, oxycodone, methadone, fentanyl, buprenorphine, and tramadol reliably. 2
- Only morphine and codeine are reliably detected on routine screening, which may lead to false negatives for hydrocodone use. 1
When Oxycodone Detection Occurs
If oxycodone appears on a confirmatory test (GC-MS or LC-MS/MS) in a patient prescribed only hydrocodone, this indicates one of three possibilities:
- Undisclosed oxycodone use - The patient is taking oxycodone from another source (most common explanation). 1
- Contamination from oxycodone impurities - Hydrocodone can be present as an impurity (up to 1%) in oxycodone pills, but the reverse (oxycodone in hydrocodone pills) has not been documented in the literature. 3
- Laboratory error - Though rare with proper confirmatory testing. 1
Critical Testing Approach
- Always order confirmatory testing with gas chromatography-mass spectrometry (GC-MS) or LC-MS/MS when results are unexpected or will impact patient management, as these methods can definitively identify specific opioids and differentiate them from structurally similar compounds. 1
- Standard immunoassay results alone should never be used to make consequential clinical decisions such as discharging patients from care, as this constitutes patient abandonment. 1
- GC-MS and LC-MS/MS are selective enough to differentiate specific opioids and metabolites from one another with detection limits typically less than 1 ng/mL. 1
Important Metabolite Considerations
- Hydrocodone is metabolized to hydromorphone (not oxymorphone), which is detectable for 1-2 days after hydrocodone use. 1
- Oxycodone is metabolized to noroxycodone and oxymorphone - these are distinct from hydrocodone's metabolic pathway. 4, 5
- The presence of noroxycodone or oxymorphone in the absence of hydrocodone metabolites confirms oxycodone use rather than hydrocodone use. 4, 5
Clinical Pitfalls to Avoid
- Never assume immunoassay results are definitive - they are screening tests only with known limitations and significant cross-reactivity issues. 1
- Obtain a complete medication history including all prescription medications, over-the-counter drugs, and supplements before interpreting any positive drug test. 1
- Discuss unexpected results with the local laboratory or toxicologist before making clinical decisions. 1, 6
- Document the medication list on the laboratory request form to aid in proper interpretation. 1
Proper Documentation and Next Steps
- If oxycodone is confirmed on GC-MS testing in a patient prescribed only hydrocodone, have a non-judgmental conversation with the patient about the results. 1
- Check the Prescription Drug Monitoring Program (PDMP) for concurrent controlled medications from other prescribers. 2
- Consider that the patient may have legitimate prescriptions from multiple providers or may be using diverted medications. 1