What does a MET (methamphetamine) result on a drug screen indicate?

What Does "MET" on a Drug Screen Mean?

A "MET" result on a drug screen indicates the detection of methamphetamine or its metabolites in the specimen, but this finding requires careful interpretation because it can result from illicit methamphetamine use, legitimate prescription medications (such as ADHD medications), over-the-counter products, or false-positive cross-reactivity with other substances 1.

Understanding the Result

What MET Detects

• Methamphetamine is detected through immunoassay screening tests that identify the drug and its metabolites in urine
• The screening test uses a common metabolite to identify the entire amphetamine class, but this approach has important limitations 1
• Standard screening immunoassays can cross-react with unrelated substances, leading to false-positive results

Critical Interpretation Considerations

A positive MET screen does NOT automatically mean illicit drug use. Several legitimate scenarios can produce this result:

1. Prescription medications: Patients taking amphetamine/dextroamphetamine for ADHD will test positive for amphetamines, which may appear as MET-positive 1

2. Over-the-counter products: The l-enantiomer of methamphetamine is found in certain nasal inhalers (like Vicks Inhaler), which can produce positive results 2

3. Cross-reactivity: Multiple commonly prescribed medications can trigger false-positives, including certain antidepressants (bupropion, trazodone), antihistamines (diphenhydramine), and other agents 3

4. Metabolic conversion: Low levels of methamphetamine may appear in urine as a trace metabolic product when amphetamine is the primary drug used 4

Clinical Action Algorithm

Step 1: Obtain Complete Medication History

• Document all prescription medications, particularly ADHD medications, antidepressants, and decongestants
• Ask about over-the-counter nasal inhalers and cold medications
• Review timing of medication use relative to the test 1

Step 2: Assess Clinical Context

Key clinical indicators that suggest true methamphetamine exposure (not false-positive):

• Tachycardia (strongly associated with confirmed methamphetamine, P < .001) 5
• Concurrent amphetamine positivity on the same screen (96% positive predictive value) 5
• Behavioral changes, agitation, or psychiatric symptoms
• Hypokalemia, elevated creatine kinase, elevated lactate, or hyperthermia (trending associations) 5

Step 3: Determine Need for Confirmatory Testing

Always obtain confirmatory testing when:

• The result doesn't correlate with clinical presentation
• No legitimate explanation exists from medication history
• Legal, employment, or significant clinical consequences depend on the result
• The patient denies illicit use despite positive screening 1

Confirmatory testing methods:

• Gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS)
• Chiral analysis to differentiate d-methamphetamine (illicit/prescription) from l-methamphetamine (OTC products) 6, 2
• Detection of d-enantiomer or mixed d- and l-enantiomers establishes controlled substance use 2

Step 4: Interpret Quantitative Results

When confirmatory testing is available:

• High methamphetamine with low amphetamine: Suggests primary methamphetamine use
• High amphetamine with trace methamphetamine (<2% of amphetamine level): Likely represents amphetamine N-methylation as a minor metabolic pathway, not polydrug use 4
• Presence of d-methamphetamine: Indicates controlled substance exposure (illicit or prescription)
• Only l-methamphetamine: Consistent with OTC nasal inhaler use 2

Common Pitfalls to Avoid

1. Never assume a positive screening test proves illicit use - immunoassays have significant false-positive rates 1, 3

2. Don't dismiss clinical concerns based solely on a negative test - timing of use, specimen dilution/adulteration, or substances not included in the panel can produce false-negatives 1

3. Recognize that drug testing cannot distinguish appropriate use from misuse of prescribed medications 1

4. Be aware that 25-40% of positive screening tests may be false-positives in some populations 5

5. Don't overlook specimen validity issues - check creatinine levels, temperature, pH, and appearance to detect dilution, substitution, or adulteration 1

When to Seek Additional Expertise

Contact the testing laboratory when:

• Test results don't match clinical findings
• You suspect use of a substance not included in the standard panel
• Interpretation is complex or has significant consequences 1

Consider referral to addiction specialist when:

• Confirmed methamphetamine use is identified
• Specimen substitution or adulteration is detected (suggests serious substance use disorder) 1
• Clinical suspicion remains high despite negative confirmatory testing