What substances are detected in a positive Urine Toxicology Screen (UTS) or Urine Toxicology Unit (UTU)?

What Shows in Urinalysis for a Positive Urine Toxicology Screen

A positive urine toxicology screen detects specific drug classes through immunoassay testing, most commonly identifying opiates/opioids, benzodiazepines, amphetamines/methamphetamine, cannabinoids (THC), cocaine metabolites, and phencyclidine (PCP), though many commonly abused substances require specialized testing not included in standard panels. 1

Standard Substances Detected on Routine Panels

Commonly Included Drug Classes

• Opiates: Standard immunoassays detect morphine and codeine, but do NOT reliably detect synthetic opioids like fentanyl or semisynthetic opioids like oxycodone 1, 2
• Benzodiazepines: Primarily detect oxazepam (a common metabolite), but frequently miss clonazepam and lorazepam which are not metabolized through the same pathway 2, 3
• Amphetamines/Methamphetamine: Detect amphetamine-type stimulants, but methylphenidate (Ritalin) is NOT detected on routine amphetamine panels 2, 4
• Cannabinoids (THC): Detect marijuana metabolites, but synthetic cannabinoids (K2, Spice) will NOT be detected 2
• Cocaine metabolites: Detect benzoylecgonine, the primary cocaine metabolite 1
• Phencyclidine (PCP): Included in many standard panels 1

Critical Substances NOT Detected by Standard Testing

Date Rape Drugs and Short-Window Substances

• Flunitrazepam (Rohypnol): Not identified in routine benzodiazepine tests; detection window only 24 hours in blood and up to 48 hours in urine 2
• GHB (gamma-hydroxybutyrate): Undetectable in urine after only 12 hours or less 2
• Ketamine: Variable detection window of 24-72 hours, requires specific testing 2

Commonly Missed Prescription and Illicit Drugs

• Fentanyl and carfentanil: Not detected by standard opiate immunoassays 2, 4
• Buprenorphine: Requires specialized testing 4
• MDMA (Ecstasy): Not detected by standard panels, requires specific testing 2, 4
• Alcohol: Not included in many standard drug testing panels despite being the most common substance associated with sexual assault 2
• Inhalants: Not detected by standard tests 2

Understanding Test Methodology and Limitations

Two-Tier Testing Approach

• Initial screening: Qualitative immunoassay tests (enzyme-linked immunoassay) provide rapid positive/negative results but are susceptible to cross-reactions causing false-positives 1, 3
• Confirmatory testing: Gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS) definitively identifies specific substances and provides quantitative concentrations 1, 3

Detection Windows

• Most drugs of abuse: 72 hours or less in urine (except marijuana) 2
• GHB: Less than 12 hours 2
• Marijuana: Can be detected for weeks in chronic users 2

Common Causes of False-Positive Results

Medications That Cross-React

• Fluoroquinolone antibiotics: Can cause false-positive opiate results 2
• Bupropion: Can cause false-positive amphetamine results 4
• Pseudoephedrine: Most commonly cited cause of false-positive amphetamine screening 4
• Dextromethorphan: Can cause false-positive results 4
• Poppy seeds: Cause false-positive morphine and codeine results on both screening AND confirmatory tests 4

Critical Clinical Interpretation Principles

Before Making Clinical Decisions

• Obtain complete medication history including all prescription medications, over-the-counter drugs, and supplements before interpreting any positive result 4
• Discuss unexpected results with laboratory personnel or toxicologist before taking action 1, 2
• Never make punitive decisions based solely on immunoassay results without confirmatory testing 5
• Request confirmatory GC-MS testing when results are unexpected, inconsistent with clinical picture, or will impact patient management 1, 2, 5

Understanding Metabolite Patterns

• Hydromorphone is a metabolite of hydrocodone, so positive hydromorphone may not indicate separate use 1
• Oxymorphone is a metabolite of oxycodone, so positive oxymorphone may reflect prescribed oxycodone 1
• Morphine can result from prescribed morphine, codeine, or heroin use 5
• 6-MAM (6-monoacetylmorphine) is the only definitive marker for heroin use, but has a very short detection window 5

Key Pitfalls to Avoid

• Assuming negative standard test excludes all substance use: Many substances require specialized testing not included in standard panels 2
• Failing to consider timing of sample collection: Most substances have short detection windows requiring immediate testing if suspected 2
• Interpreting immunoassay results as definitive: These are screening tests only with known cross-reactivity issues 1, 4
• Not knowing which specific drugs are included in your laboratory's testing panel: Panels vary by institution and must be understood for proper interpretation 1, 2
• Testing for substances when results won't affect management: This adds unnecessary costs without clinical benefit 1