GC/MS Confirmatory Testing
Screening and Confirmatory Testing
Author: William McConnell (Scientist in Charge of Biochemistry: Clinipath Pathology)
All urines are first checked by a screening test using immunoassay. This is an analytical process that uses specific antibodies to detect compounds of interest. When screening for drugs of abuse we have specific cut-off levels defined by the Australian standard AS: 4308.
The AS: 4308 standard also requires confirmatory testing to be done on samples where the screening test detects a compound above the specific cut-off value.
Confirmatory testing by Gas Chromatography with Mass Spectrometry (GC/MS) or an approved equivalent should be done on all samples where a compound is detected by the screening test. The GC/MS allows us to look for specific compounds and can determine if certain drugs are present and if this is consistent with any stated medication. This also allows us to distinguish between legally available compounds and illicit drugs.
Confirmatory Testing
Opiates
Codeine and Morphine are the main Opiates looked for during confirmatory testing. In addition 6-Monoacetyl Morphine (Heroin metabolite) can be looked for if the screening test indicates this compound may be present. Codeine breaks down to Morphine in the body and the presence of both in the urine is consistent with the use of a medication containing Codeine.
Heroin breaks down to 6-Monoacetyl Morphine and then to Morphine. If 6-Monoacetyl Morphine is detected by confirmatory testing above the cut-off level of 10 ug/L this result is consistent with recent Heroin use. Very high levels of Morphine are usually seen with the use of Morphine or Heroin. Prescription access to Morphine is very restricted and claims of its legal use may require verification.
Poppy seed ingestion can also lead to detectable levels of Morphine in the urine. If poppy seeds have been ingested, Morphine is usually less than 2000 ug/L however Morphine has been reported as high as 11571 ug/L after poppy seed consumption.
The cut-off level for confirmatory testing for Codeine and Morphine in urine samples is 300 ug/L.
Amphetamines
The Amphetamine type substances are a large family of compounds that include both lawfully available and illicit drugs. Ephedrine and Pseudoephedrine are found in “Cold and Flu” medication and can be obtained over the counter from a pharmacist. The cut-off level for the detection of Ephedrine and Pseudoephedrine is 500 ug/L.
Phentermine and Amphetamine (also called Dexamphetamine) are available on prescription. The confirmatory cut-off levels are 500 ug/L and 150 ug/L respectively. Both can also be drugs of abuse and claims of legal use should be verified.
Methamphetamine (ICE, Crystal Meth), MDMA (Ecstasy) and MDA are not present in medications and their use is unlawful in Australia. The confirmatory level for these compounds is 150 ug/L.
Cannabis
The Cannabis cut-off for GC-MS is 15 ug/L which is much lower than the cut-off for the immunoassay screening test. This is because the screening test looks for a family of chemicals produced as a result of Cannabis use. The GC-MS specifically looks for the 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (Carboxy-THC) which is the main by-product of cannabis use found in the urine. Carboxy-THC above the cut-off level of 15 ug/L is consistent with Cannabis use.
Cocaine
The GC-MS for Cocaine looks for two main breakdown products of cocaine metabolism which are Benzoylecgonine and Ecgonine methyl ester. The presence of either of these compounds above the cut-off level of 150 ug/L is consistent with recent Cocaine use.
Benzodiazepines
Benzodiazepines are a common prescription medication. GC-MS or LC-MS confirmatory testing can determine if compounds detected in a urine sample are consistent with Benzodiazepine use. In addition the results can be compared to the stated medication to indicate if results are consistent. Different Benzodiazepine medications will result in different breakdown products being detected in the urine sample. The cut-off level for urine Benzodiazepines in confirmatory testing depends on the compound and may be 100 ug/L or 200 ug/LLabels: Urine Drug and Alcohol Screen
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