Fast Fact and Concept #110: Urine drug testing

Author(s): Mapa M; Arnold R

Background
Urine drug testing (UDT) is widely used for testing for opioids and illicit drugs. There are two types of UDT: a screening test and a confirmatory test. The screening test uses an immunoassay to look for the parent drug and/or metabolite. Most UDTs screen for marijuana, cocaine, opiates, PCP, amphetamines, while some also test for benzodiazapines and methadone. The confirmatory urine drug test is done by gas chromatography/mass spectrometry (GC/MS) or high-performance liquid chromatography (HPLC); this test is highly specific and is typically used when testing for the presence of a specific drug is needed.

UDT Interpretation
A UDT cannot tell the amount of drug ingested/used or the time of use or the source of drug (intravenous vs. oral vs. inhaled). Detection time of a substance in urine is typically 1-3 days. The rate of excretion varies depending on differences in metabolism/ urinary function. Thus, obtaining history as to when a suspected drug was last used needs to be correlated to the timing of the test. Lipid-soluble drugs (e.g. marijuana) may remain in body fat and be detectable for a week or more.

Typically the screening immunoassay UDT detects the amount of drug present in urine above a predetermined "cutoff" concentration. Thus, a substance may be present, but if the concentration of that drug is below the "cutoff", the result will be negative. If you suspect drug use or desire the confirmation of this substance, ask the urine to be tested with a "no cutoff" or "no threshold testing" or ask for a confirmatory test with GC/MS or HPLC.

If specimen tampering is suspected, ensure the urine is compatible with human physiology. The urine temperature should be 90-100 ?F; pH between 4.5 & 8.0; and a spot check of urinary creatinine greater than 20mg/dL. A creatinine less than 20mg/dL it is considered dilute; less than 5mg/dL the sample should be discarded since it is not consistent with human urine.

The screening immunoassay test has limited specificity for opiates. The test cannot differentiate morphine from codeine (natural occurring opiates )and will not reliably detect synthetic or semi-synthetic opioids. A confirmatory test is required to test for all opioids.

Knowledge of opiate metabolism is needed for UDT interpretation. For example, codeine and heroin are both metabolized to morphine, through different pathways and different intermediary metabolites. A prescription for codeine may yield an appropriate positive result for codeine and morphine in the urine. However, if codeine is prescribed and only morphine is found in drug testing, the most consistent interpretation is the unknown use of morphine or heroin. Prescribed morphine will result in only morphine in a sample and not codeine.

The presence of marijuana is detected by the presence of tetrahydorcannabinol (THC), its active ingredient. The screening immunoassay UDT is unable to distinguish between smoked marijuana and the synthetic preparation, dronabinol (Marinol).

False positive immunoassays are the result of cross reactivity. Quinolones, specifically levofloxacin and ofloxacin, may give a positive result for opiates.

The cost of a UDT differs from lab to lab and especially in the number of substances tested. The screening test costs between $69 to $148; the confirmatory test ranges from $92 to $165.

References:
Gourlay D, Heit H, Caplan Y. Urine Drug Testing in Primary Care: Dispelling the Myths and Designing Strategies. Monograph PharmaCom Group, Inc. c 2002.

Fast Facts were edited by David Weissman MD, Palliative Care Center, Medical College of Wisconsin until January 2007.  For comments/questions write to the current editor, Drew Rosielle MD: drosiell@mcw.edu. The complete set of Fast Facts is available at EPERC: www.eperc.mcw.edu

Copyright/Referencing Information: Users are free to download and distribute Fast Facts for educational purposes only. Citation for referencing: Mapa M and Arnold R. Fast Facts and Concepts #110. Urine drug testing. April 2004. End-of-Life/Palliative Education Resource Center www.eperc.mcw.edu.

Disclaimer: Fast Facts provide educational information, this information is not medical advice. Health care providers should exercise their own independent clinical judgment. Some Fast Fact information cites the use of a product in dosage, for an indication, or in a manner other than that recommended in the product labeling. Accordingly, the official prescribing information should be consulted before any such product is use.

Creation Date: 4/2004

Purpose: Instructional Aid, Self-Study Guide, Teaching

Audience(s)

ACGME Competencies: Medical Knowledge, Patient Care, System-based Practice

Keyword(s): Pain>opioids; psychiatric disorders

Specific Disease and Organ System Category(s): Psychiatric Disorders