Urine Drug Tests: Ordering and Interpretation

 

Urine drug testing is an essential component of monitoring patients who are receiving long-term opioid therapy, and it has been suggested for patients receiving long-term benzodiazepine or stimulant therapy. Family physicians should be familiar with the characteristics and capabilities of screening and confirmatory drug tests. Immunoassays are used for initial screening and can give false-positive and false-negative results. All results are considered presumptive until confirmatory testing is performed. False-positive results have significant implications for a patient's pain treatment plan, and false-negative results can be a missed opportunity to detect misuse. Urine drug testing is an essential component of monitoring patients who are receiving long-term opioid therapy, and it has been suggested for patients receiving long-term benzodiazepine or stimulant therapy. Family physicians should be familiar with the characteristics and capabilities of screening and confirmatory drug tests. Immunoassays are qualitative tests used for initial screening of urine samples. They can give false-positive and false-negative results, so all results are considered presumptive until confirmatory testing is performed. Immunoassays for opioids may not detect commonly prescribed semisynthetic and synthetic opioids such as methadone and fentanyl; similarly, immunoassays for benzodiazepines may not detect alprazolam or clonazepam. Immunoassays can cross-react with other medications and give false-positive results, which have important implications for a patient's pain treatment plan. False-negative results can cause missed opportunities to detect misuse. Urine samples can be adulterated with other substances to mask positive results on urine drug testing. Family physicians must be familiar with these substances, the methods to detect them, and their effects on urine drug testing.

Urine drug testing is an important part of managing long-term opioid therapy. With the recent increase in deaths caused by opioid overdoses, several federal and state regulations have been enacted that recommend or require urine drug testing in patients receiving long-term opioid therapy. Similar guidance has been suggested for patients receiving long-term benzodiazepine or stimulant therapy. The purpose of urine drug testing is to monitor compliance with prescribed therapy and detect the use of nonprescribed and illicit substances, especially heroin and nonprescribed opioids and benzodiazepines, all of which can increase the risk of a fatal overdose.1,2 Weak evidence suggests that random urine drug testing decreases the use of illicit drugs in patients receiving long-term opioid therapy.3

WHAT IS NEW ON THIS TOPIC

Several federal and state regulations have been enacted that recommend or require urine drug testing in patients receiving long-term opioid therapy. Similar guidance may apply to patients receiving long-term benzodiazepine or stimulant therapy.

Ingestion of food containing poppy seeds will not cause a positive urine drug test result. Similarly, passive inhalation of marijuana smoke is unlikely to cause a positive tetrahydrocannabinol urine test result.

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SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendationEvidence ratingReferences

Urine drug testing can be used to monitor compliance with prescribed therapy and detect the use of nonprescribed and illicit substances, especially opioids, benzodiazepines, and heroin.

C

1

Immunoassays are subject to false-positive and false-negative results. All positive and any unexpected negative results must be verified by confirmatory testing.

C

9

Casual dietary ingestion of poppy seeds does not cause a positive result for opioids on urine drug testing.

C

22

Casual exposure to cannabis smoke does not cause a positive result on urine drug testing.

C

23


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendationEvidence ratingReferences

Urine drug testing can be used to monitor compliance with prescribed therapy and detect the use of nonprescribed and illicit substances, especially opioids, benzodiazepines, and heroin.

C

1

Immunoassays are subject to false-positive and false-negative results. All positive and any unexpected negative results must be verified by confirmatory testing.

C

9

Casual dietary ingestion of poppy seeds does not cause a positive result for opioids on urine drug testing.

C

22

Casual exposure to cannabis smoke does not cause a positive result on urine drug testing.

C

23


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented

The Author

NEELIMA KALE, PhD, MD, MBA, FAAFP, is an assistant professor in the Department of Family and Community Medicine at the University of Texas Southwestern Medical Center, Dallas. She also serves as the medical director of the Parkland Family Medicine Residency Clinic in Dallas.

Address correspondence to Neelima Kale, PhD, MD, MBA, UT Southwestern, 5959 Harry Hines Blvd., Ste. 720, Dallas, TX 75390-9165. Reprints are not available from the author.

Author disclosure: No relevant financial affiliations.

References

show all references

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