Opiate Interpretation for Pain Medicine

Opioids are a large class of medications commonly used to relieve acute and chronic pain or help manage opioid abuse and dependence. Medications that fall into this class include: buprenorphine, codeine, fentanyl, hydrocodone, hydromorphone, methadone, morphine, oxycodone, oxymorphone, tapentadol, tramadol, and others. 

Type of Opioids

• Natural opioids (opiates)
  • Morphine
  • Codeine
  • Thebaine
• Semisynthetic opioids
  • Heroin
  • Hydromorphone
  • Hydrocodone
• Fully synthetic opioids
  • Methadone
  • Fentanyl
  • Tramadol
  • Pethidine
  • Levorphanol
  • Dextropropoxyphene
• Opioid antagonists & agonist/antagonist
  • Buprenorphine
  • Naloxone

The American Society of Interventional Pain Physicians guideline states that urine drug testing must be implemented at initiation and during chronic pain management therapy. CDC issued new recommendations for prescribing opioid medications for chronic pain in March 2016 that include urine drug testing before starting opioid therapy and at least annually. The purpose of urine drug testing is to verify adherence to prescribed medications, identify undisclosed drugs, and discourage drug misuse, abuse, and diversion.

Opioids are readily absorbed from the gastrointestinal tract, nasal mucosa, lungs, and after subcutaneous or intermuscular injection. Opioids are primarily excreted from the kidney in both free and conjugated forms. The detection window for most opioids in urine is approximately 1 to 3 days with longer detection times for some compounds such as methadone.

Opiate immunoassays usually test for morphine, morphine-3-glucuronide, and codeine in human urine and gives a positive result if any of these opiates are present. They can also detects synthetic opiates related to morphine, such as hydromorphone, and high concentrations of the analgesic meperidine and the narcotic antagonist nalorphine. In general, opiate immunoassays do not reliably detect oxycodone, oxymorphone, meperidine, and fentanyl. Positive results for specimens containing other compounds structurally unrelated to opiates have not been observed. Immunoassay opiate cutoff for pain medicine compliance is 300 ng/mL.

However, if immunoassay results are inconsistent with prescribed therapy, the patient’s urine sample should be further analyzed by gas chromatography mass spectrometry (GC/MS) or liquid chromatography tandem MS (LC/MS/MS).  One study have demonstrated that the expected opioid was detected in 55% of patients but missing in 10%, while illicit drugs were detected in 20% and an unexpected opioid was detected in 15%. Primary care physicians and pain medicine specialists often have difficulty interpreting urine drug screen results when results differ from prescribed therapy. The following table can help clinical laboratories answer their questions. 

Interpretation Guidelines

References

Nagpal G, etal. Interpretation of Urine Drug Screens: Metabolites and Impurities. JAMA 2017;318:1704-5. 

Michna et al. Clin J Pain. 2007;23:173-9.