Episode Details

Episode 157: Urine Testing

This episode includes the pitfalls of urine tests, how to detect adulterated urine, and more.  

Written by Janelli Mendoza, MSIV, Ross University School of Medicine. Editing by Hector Arreaza, MD. Comments by Carol Avila, MD.

You are listening to Rio Bravo qWeek Podcast, your weekly dose of knowledge brought to you by the Rio Bravo Family Medicine Residency Program from Bakersfield, California, a UCLA-affiliated program sponsored by Clinica Sierra Vista, Let Us Be Your Healthcare Home. This podcast was created for educational purposes only. Visit your primary care provider for additional medical advice.

Introduction: Urine drug screenings are valuable tools used every day by physicians to monitor illicit substance use, as well as proper use or misuse of prescription drugs. However, studies suggest that physicians using “clinical judgment” on who and when to test is often wrong and confounded by implicit racial bias. The implications of this are an inappropriate discontinuation of treatment.

For example, a study by Gaither, Gordon, and Crystal et. al found that compared to white patients, black patients were 10% more likely to undergo urine drug screening. In addition, they were 2-3 times more likely to have long-term opioid medication abruptly discontinued as a result of a UTOX positive for marijuana.

False positive urine tests:

Before getting into the current guidelines, let’s discuss the interpretation of Urine Drug Screenings. It’s important to be aware of prescription drugs that may cause false positives:

· Bupropion, labetalol, pseudoephedrine, trazodone → Amphetamines

· HIV antivirals, sertraline → Benzodiazepines

· HIV antivirals, NSAIDs, PPI’s → Cannabinoids

· Diphenhydramine, Naloxone, Quetiapine, Quinolones, Verapamil → Opioids

· Dextromethorphan, diphenhydramine, ibuprofen, tramadol, venlafaxine → Phencyclidine

Tampering of urine: Other factors to consider are the tampering of collected urine. The tampering of collected urine may include diluting the urine, or adding other chemicals and substances. Laboratory results that should prompt consideration of adulteration are: Creatinine <20 mg/dL, pH <3 or >11, Specific gravity <1.001 or > 1.035, Temp <90 F or > 100 F

How long urine tests are positive:

The detection window for common substances in urine drug screenings are as follows:

· Amphetamines: 2-3 days

· Cocaine: 1-2 days

· Opioids: 1-3 days, but up to 14 days if the patient is on methadone.

· Phencyclidine: up to or less than 1 week, may be longer if chronic use.

Cannabinoids are a little different as the THC component builds up and is stored in adipose tissue. Therefore, a patient's weight, body fat percentage, exercise level, and diet can all influence the detection window. This is more so an issue for chronic daily users.

· For single-time use: 2-3 days.

· Daily use: 2-4 weeks

· Chronic heavy use: >6-8 weeks as we said, the exact time will be influenced by many factors depending on how long it takes to deplete THC molecules stored in adipose tissue.

Monitoring use of prescription drugs:

Dr. John Hayes and Dr. Kristen Fox at the Department of Family Medicine and Community Medicine College of Wisconsin have developed a patient-centered approach in utilizing urine drug screenings for monitoring the use of controlled prescription drugs. If physicians should not test based on suspected misuse of medications, then when should they test? 

The frequency of screening should be determined based on a patient’s risk for substance use disorder. This will be determined by use of evidence-based tools such as a risk calculator. On MD calc, clinicians can find the ORT (Opioid Risk Tool for Narcotic