An unexpected result is a question to investigate, not a conclusion about the patient. The clinician should pause, verify what was ordered, discuss the finding, and use definitive testing when the answer will change care.
1. Confirm the expectation
Was the medication supposed to be taken daily or as needed? When was the last dose? Which nonprescribed substances did the patient report? An apparent discrepancy may reflect an incorrect assumption.
2. Review the actual panel
Many screens test drug classes and omit important substances. Fentanyl, buprenorphine, methadone, oxycodone, and some benzodiazepines may require separate assays. A negative result for a generic class may not address the prescribed drug.
3. Consider timing and concentration
Collection time, dose, intermittent use, metabolism, hydration, kidney function, and cutoff affect detection. A urine concentration cannot be translated directly into dose or impairment.
4. Check metabolites and cross-reactivity
A detected drug may be a metabolite of another medication. Immunoassays can react with structurally similar prescriptions or over-the-counter products. Consult the laboratory’s assay documentation rather than relying on a generic list.
5. Review specimen validity and process
Dilution, substitution, adulteration, mislabeling, transport error, or a wrong-patient event can affect interpretation. Review creatinine or validity findings, collection notes, and chain of custody when relevant.
6. Discuss without accusation
Ask open questions and explain the limitation. A patient may have stopped a medication because of side effects, taken it differently, received emergency treatment, or used an unreported substance. Neutral discussion can resolve the discrepancy and preserve care.
7. Order definitive testing when needed
Confirm when the presumptive result is unexplained and will drive a major clinical or nonclinical decision, or when a specific drug is not reliably detected by the screen. Use the original specimen when appropriate.
8. Use the result to improve safety
Possible responses include medication review, more frequent follow-up, naloxone, counseling, treatment referral, or changing therapy. CDC advises against dismissing patients solely because of a toxicology result.
Sources
Medical review: October 29, 2026.