Urine Drug and Alcohol Screens
Author: William McConnell (Scientist in Charge Biochemistry: Clinipath)
What drugs do we look for?
The main drugs looked for in a standard urine drug and alcohol screen are:
Alcohol
Amphetamines (includes dexamphetamine, methamphetamine and ecstasy
Benzodiazepines
Cannabis (THC
Cocaine
Methadone
Opiates, including 6-monoacteyl morphine (6-MAM
What are the cut-off levels for a positive result?
The following cut-off levels are used for reporting drugs of abuse in urine.
Alcohol 0.02% (zero tolerance cut-off); 0.05% (common cut-off)
Amphetamines (300 ug/L)*
Benzodiazepines (200 ug/L) *
Cannabis (50 ug/L) *
Cocaine (300 ug/L as metabolite) *
Opiates (300 ug/L) *
6-MAM (10 ug/L) *
Methadone (100 ug/L as metabolite EDDP)
* cut off level taken from the AS/NZ 4308:2008 standard.
How long do these drugs stay in the system?
Some drugs are cleared rapidly from the system while others can persist for a long time. Regular use of a drug can also mean it stays in the system longer.
As a guideline most common drugs have the following clearance rates.
Alcohol 12 hours
Amphetamines 2-4 days
Benzodiazepines 3-10 days (up to a month if heavy use
Cannabis up to 6 weeks
Cocaine 2-4 days
Methadone 3-5 days
Opiates 2-4 days
Will passive smoking lead to a positive result for Cannabis?
The cut off level for Cannabis has been chosen to exclude passive smoking as a cause for a positive result.
A donor will not test positive for Cannabis as a result of passive smoking unless the exposure has been extreme. The donor will be aware of such exposure.
What does it mean if the urine is dilute?
A chemical called creatinine is present in urine and this is measured to see if the sample is dilute. If the donor drinks too much water, the urine may become very dilute.
A dilute sample will still be tested and positive results will be reported. Negative results will be marked as unsuitable and a repeat sample will be requested.
If a donor continues to present dilute samples with no reasonable medical explanation then intentional dilution to avoid detection must be considered.
What does it mean if the temperature check fails?
A freshly produced urine sample should be at body temperature.
If the temperature is outside expected values then sample substitution or tampering must be considered. The temperature check may also fail if an insufficient volume of sample is produced.
If the temperature check fails it will be noted on the report and a repeat collection will be recommended.
Is the sample checked for masking agents?
All urine samples are checked in the laboratory for compounds commonly used to interfere with drug testing. If interfering compounds are detected this will be indicated on the report.
What is the difference between a screen and a confirmation?
The initial screen for drugs uses an immunoassay that looks for selected drug classes. Positive screening results can be caused by prescription and over the counter medications and so it is important to note any recent medications on the chain of custody form before the testing is done.
Confirmatory testing is done using a technique called Gas Chromatography with Mass Spectrometry (GC-MS). This is a highly accurate technique that is able to specifically identify and quantitate individual drugs that may be present.Labels: Urine Drug and Alcohol
|