PATHCHAT Edition No. 41
Please contact your local Ampath pathologist for more information.
Authors: Dr. N. Lutchman and Dr. M. du Plessis
Introduction
🔹 Why is DOAS Important?
- Used in workplace drug testing, professional sports, emergency departments, and trauma units.
- Helps guide medical management in patients with altered mental states or suspected drug overdose.
✅ Ampath’s Standard Urine Screening Panel Includes:
- Amphetamines.
- Benzodiazepines.
- Cannabis.
- Cocaine.
- Mandrax (Methaqualone).
- Methadone.
- Opiates.
- Confirmatory tests for Ecstasy (MDMA), Methamphetamine (Tik), and Methcathinone (CAT).
📌 Barbiturates are tested as part of the urine toxic screen with benzodiazepines and can also be requested separately.
DOAS Screening & Confirmatory Testing
✅ Types of DOAS Testing Available at Ampath:
- Qualitative Screening (Dipstick Testing – Immunochromatography).
- Quantitative Immunoassay Testing (Standard Screening).
- Confirmatory Testing Using Tandem Mass Spectrometry:
- Gas Chromatography-Mass Spectrometry (GC-MS/MS).
- Liquid Chromatography-Mass Spectrometry (LC-MS/MS).
✅ Key Considerations:
- Immunoassays have high sensitivity but lower specificity for certain drug classes (e.g., opiates, amphetamines).
- A positive screening result is considered presumptive and must be confirmed by mass spectrometry.
📌 Confirmatory testing is essential to differentiate between similar compounds and rule out false positives.
Specimen Collection & Integrity Checks
✅ Preferred Sample:
- Urine is the preferred specimen due to its ease of collection and longer drug detection window.
✅ Specimen Integrity Testing:
- Urine pH should be between 4.5 and 8.0.
- pH <3 or >11 suggests adulteration.
- Creatinine levels <20 mg/dL may indicate dilution.
📌 Tampering methods include adulterants, substitution, and dilution; hence, supervised collection and integrity checks are essential.
Cut-Off Levels & Drug Detection Windows
🔹 Ampath follows the Substance Abuse and Mental Health Administration (SAMHSA) cut-off levels for adult drug screening.
- Values below the cut-off level are reported as negative.
- Detection windows vary by drug type and usage frequency.
📌 There are four major drug groups tested in DOAS: Psychostimulants, Hallucinogens, Anaesthetics, and Analgesics.
1. Psychostimulants
Amphetamines (Speed, Methamphetamine – Tik)
✅ Key Features:
- Cleared rapidly from blood; urine is the preferred specimen.
- Detected in urine for up to 4 days post-use.
- Cross-reactivity with pseudoephedrine, ephedrine, phenylephrine, and phentermine.
📌 Screening detects MDMA (Ecstasy) and methamphetamine (Tik) to varying degrees.
✅ Cut-Off Level: 1,000 ng/mL
Methamphetamine (Tik, Crystal Meth, Ice)
✅ Key Features:
- Metabolized to amphetamine.
- Methamphetamine-positive urine usually contains amphetamine as well.
- Cross-reactivity with MDMA (Ecstasy).
📌 LC-MS/MS can distinguish methamphetamine from MDMA.
✅ Cut-Off Level: 1,000 ng/mL
Cocaine (Coke, Crack)
✅ Key Features:
- Metabolized to benzoylecgonine (detected in urine).
- Highly specific immunoassay – false positives are uncommon.
- Detected for up to 2 days in occasional users, up to 7 days in chronic users.
✅ Cut-Off Level: 300 ng/mL
2. Hallucinogens
Cannabis (Marijuana, Dagga, Grass, Pot)
✅ Key Features:
- Primary psychoactive component: Δ9-Tetrahydrocannabinol (THC).
- Highly lipophilic, leading to prolonged excretion.
- Detected for up to 7 days in occasional users, up to 30 days in chronic users.
- False positives with Efavirenz (HIV drug) and some proton pump inhibitors (PPIs).
📌 Synthetic cannabinoids are NOT detected by standard urine assays.
✅ Cut-Off Level: 50 ng/mL
Lysergic Acid Diethylamide (LSD – Acid)
✅ Key Features:
- Minimal amounts excreted in urine.
- Short detection window (~4 hours).
- Confirmatory testing available (LC-MS/MS only).
Phencyclidine (PCP – Angel Dust)
✅ Key Features:
- Low specificity of immunoassay results in false positives.
- Detected for 4–7 days post-use.
- False positives with diphenhydramine (Benadryl) and dextromethorphan.
✅ Cut-Off Level: 25 ng/mL
3. Anaesthetics
Barbiturates (Downers, Barbs)
✅ Key Features:
- Short- or long-acting (detectable for 1–14 days).
- Often abused to induce sleep after stimulant use.
✅ Cut-Off Level: 200 ng/mL
Benzodiazepines (Tranquilizers, Sleeping Pills)
✅ Key Features:
- Commonly prescribed – difficult to distinguish abuse from therapeutic use.
- Detected for 1–7 days; diazepam metabolites may persist for weeks.
- Roche immunoassay cross-reacts with Alprazolam (Xanax), Clonazepam, Midazolam, and Flunitrazepam (Rohypnol).
- Sleeping aids (Zolpidem, Zopiclone) are NOT detected by this assay.
✅ Cut-Off Level: 2,000 ng/mL
4. Analgesics
Opioids (Morphine, Heroin, Codeine, Synthetic Opioids)
✅ Key Features:
- Class includes natural (morphine, codeine), semi-synthetic (oxycodone, hydromorphone), and synthetic opioids (fentanyl, methadone).
- Immunoassays detect morphine, heroin, and codeine.
- Synthetic opioids (fentanyl, oxycodone) require specific assays.
- Poppy seeds do NOT cause false positives when using SAMHSA cut-offs.
✅ Cut-Off Level: 2,000 ng/mL
Mandrax (Methaqualone – White Pipe, Buttons)
✅ Key Features:
- Commonly abused in South Africa.
- Often mixed with cannabis or smoked alone.
✅ Cut-Off Level: 300 ng/mL
Conclusion
✅ Urine is the preferred sample for DOAS due to longer drug detection times.
✅ Screening results must be confirmed by mass spectrometry for legal or forensic use.
✅ Specimen integrity tests (pH, creatinine) ensure sample validity.
✅ Specific immunoassays are required for synthetic opioids and designer drugs.
📌 DOAS is an essential tool in medical management, workplace drug testing, and forensic investigations.