What Is A Drug Screen

Drug screening involves one or more analytical techniques used to identify specific drugs or their metabolites in a biological matrix. Screens can be general in that they attempt to identify a wide range of illicit and therapeutic substances; or they may be selective by only identifying certain drug groups. There is no simple process that can identify all drugs. Screening processes attempt to identify commonly abused substances, however there are many drugs that cannot be readily identified by any routine process.


What Is The Difference Between Qualitative And Quantitative Drug Testing?

Routine drug analysis is qualitative - we simply report the presence of drugs in a specimen. The amount of drug detected in urine (a drug level) does not usually provide any useful information to a clinician. One cannot determine time of ingestion, amount ingested or pharmacological effect from a urine drug result. It is therefore a waste of resources to measure any level in urine if the clinician or counsellor merely wants to know if a drug is present. There are however, some exceptions, as explained below. Quantitative analysis is carried out for selected drug groups. Medico-legal drugs of abuse testing requires us to determine a concentration of drug or metabolite.


Testing For Cannabis

Testing for Cannabis involves two analytical techniques, immunoassay as a primary screen, followed by the confirmation test using gas chromatography/mass spectrometry. The second test is quantitative for two reasons. Firstly, we use internationally accepted reporting levels or cutoffs for Cannabis, currently set at 15 ug/L (15ng/mL). In other words, if a patient has a level of 14 ug/L, the result is deemed to be negative. Secondly, many patients are undergoing treatment for Cannabis dependence or they are on probation for drug related offences. Periodical measurement of urinary Cannabinoids allows the counsellor to see if a patient is reducing Cannabis intake.


Passive Smoking

The issue of passive smoking - inadvertent inhalation of sidestream smoke from other people in the vicinity, has been addressed adequately in the scientific literature. The reporting levels used in the Toxicology Unit have been set such that any positive result reported for Cannabis could not have occurred through passive inhalation.


Medico-Legal Drugs Of Abuse Testing

Routine drug testing for methadone and other treatment programs is to be used for clinical purposes only. Our results are an adjunct to patient treatment and compliance. In general the results of clinical testing should not be used as evidence in a court of law or for any legal purposes. Medico-legal testing must be requested when a patient or client is involved in any legal matter. Stricter protocols are used in the testing procedures such that laboratory evidence can withstand any legal challenge.

Medico-legal testing is conducted according to Australian Standard AS/NZS 4308 "Procedures for the collection, detection and quantitation of drugs of abuse in urine". Copies of this document are available from Standards Australia or by downloading from their web site www.standards.com.au.



Why Do We Analyse Urine Rather Than Blood Or Serum?

Urine is the preferred biological fluid used in drug testing for the following reasons:

  • The majority of drugs are excreted in urine
  • Drugs concentrate in urine
  • There is usually ample specimen for analysis
  • Collection is non-invasive and carries a lower risk of transmission of Hepatitis or HIV than blood.
  • Urine contains fewer interfering endogenous substances than blood.
  • Urine has the widest window of detection of all biological fluids. This has the advantage of identifying any recent drug use (hours to days).



What Drugs Are Not Detected In A Routine Drug Screen?

Many therapeutic or illicit substances do not show up in routine drug screens. Drugs that have been removed from the Australian market may not be identified. Some of these can be identified using more sophisticated techniques. You are advised to contact the Senior Scientist about these substances. Examples of drugs not identified by routine procedures are shown below.

  • Anabolic steroids
  • Antihistamines - some
  • AZT
  • Buprenorphine
  • Chloral hydrate
  • Diuretics
  • GHB
  • Ketamine
  • Laxatives
  • LSD
  • Non-steroidal antiinflammatories (NSAIDS)
  • Phencyclidine (PCP)
  • Psilocybin
  • Salicylates
  • Zolpidem


What Drugs Are Not Routinely Reported

  • Caffeine
  • Theobromine (from chocolate)
  • Nicotine
  • Low levels of Paracetamol


How Long Does It Take To Conduct A Routine Drug Screen?

Subject to normal workloads, specimens received by early afternoon are logged into the system that day and preliminary testing commenced. Preliminary results are ready after 2.00 pm the following working day. If no further confirmation or special tests are required, final printed reports will be posted 2 working days after receipt of sample. An abbreviated list of results will be posted with individual reports. This summarises all results from your clinic printed that day. Some specimens take longer to analyse. For example if confirmations are required for Cannabis, Benzodiazepines, Amphetamine, or Morphine/Codeine ratios, then these tests may take a few working days after initial screening tests have been performed.