Analysis of urine specimens for drugs of abuse only gives information about current or recent drug usage. A urine specimen taken more than 2-3 days after a period of 'drug abuse' is likely to be negative on screening for most substances. Cannabis is the notable exception to this, and can remain at detectable concentrations in urine for several weeks.

The approximate detection times for some drugs of abuse are listed below. There is a lot of variation from one individual to another and detection will depend on the dose administered, the frequency and route of administration, the concentration of the urine and the speed at which the drug is broken down and removed from the body.

Drug	Length of time it can be detected in urine
Alcohol*	up to 1 day (ethanol); up to 5 days (ethyl glucuronide)**
Amphetamines & Ecstasy	1-3 days Amphetamine, ecstacy; 1-6 days Methylamphetamine ("ice")
Barbiturates	1-3 days***
Benzodiazepines	Days to weeks****
Cannabis (THC)	up to several weeks (dose and history dependant)
Cocaine	1-3 days
Codeine	1-3 days
Dihydrocodeine	1-3 days
Heroin (morphine)	2-3 days*****
Methadone	1-3 days

* Testing for ethanol (alcohol) in urine has little value in either a clinical or legal context. Ethanol is not uncommonly produced by the action of yeast on urinary sugars. There are documented cases of production both in the body and during storage and transport. It is also possible for any levels of ethanol to be metabolised away by other microbial interactions.

** Ethyl glucuronide is a metabolite of ethanol consumption which may be detected for a longer period than ethanol itself. However, it is also potentially subject to false positives and false negatives as a result of bacterial metabolism.

*** Barbiturates have been steadily removed from the Australian market over the last two decades and are rarely encountered.

**** Benzodiazepine metabolism is complex and dependant on dosage, enzymatic activity, concurrent metabolism of unrelated compounds, and the specific compound. Single use of some low dose, shorter acting benzodiazepines may result in detection times of 1-3 days. Long term usage of benzodiazepines such as Diazepam may lead to detection times in excess of a month.

***** Heroin is rapidly metabolised by the body and is not usually detected in urine. The major initial metabolite (6-acetylmorphine) normally disappears from the urine in less than 24 hours. The final breakdown product (morphine) is usually detectable for 2-3 days, although levels are generally low after 2 days and may be difficult to interpret.

Drugs of abuse can also be detected in other body fluids such as saliva but with saliva the period of detection is considerably shorter than in urine.

To detect or exclude the presence of abused and/or illegal drugs. This may be carried out for a number of reasons including a pre-employment screen or to comply with a drug rehabilitation programme.

A result should not be reported as 'positive' from a screening test alone. A non-negative result on a screening test only implies the possible presence of the drug, closely related compounds or substances causing a false positive. Results from this type of testing should be reported as “non-negative”, “suspected”, “presumptive” or some similar way that does not imply proof of detection. Use of a screening test without a confirmation is of limited use. Non-negative screening results of clinical or legal significance should be subjected to confirmatory testing.

A positive confirmatory test will unambiguously identify the drug present, differentiate it from common related compounds and eliminate the possibility of false positive results. A drug detected in a confirmatory test indicates that the concentration of drug present is greater than a specified cut-off concentration for that particular drug. Many Australian laboratories use the same concentration to define a positive result and conform to the Australian/New Zealand Standard AS/NZS 4308 guidelines. Medico-legal testing should be collected by accredited collectors to this Standard and only be tested by laboratories with this level of accreditation.

The sensitivity of drug detection will be reduced in dilute urine specimens. At concentrations below the cut-off limit, the drug will normally be reported as not detected.

Certain foods and prescribed drugs can interfere and give positive results with the initial screen for certain drug groups (e.g. taking codeine or eating poppy seed bread can give a positive opiate result) and for this reason positive results should always be confirmed by a second, more accurate laboratory method before they are reported. The laboratory should also be available to comment on a positive drug confirmation. In the above example, detection of morphine from either codeine or poppy seed is likely and may require interpretation.

Codeine is an opiate drug and will therefore give a positive opiate test; it is common in prescribed painkillers and many cold and flu preparations contain either codeine, pholcodine or dihydrocodeine, all of which will register a positive screening result. Most Australian laboratory drug screens have a second confirmatory step that will allow codeine to be identified and reported as such. Pholcodine and dihydrocodeine are not usually reported.

There are numerous reasons why someone might spike a drink; the most common reasons are for amusement, to carry out a sexual assault, or for theft. The most common drug used in drink spiking is additional alcohol. Some of the so called 'date rape' or 'drink spiking' drugs such as GHB (gammahydroxybutyrate) act very quickly and pass out of the body within several hours. Others, including ketamine and sedatives such as zolpidem and the benzodiazepines may only be detectable for a few days. This rapid clearance from the body makes it important that medical advice is sought as quickly as possible and that a urine specimen is collected preferably within 6-12 hours. Other than the benzodiazepines, most 'drink spiking' drugs are often only looked for in specialised or forensic laboratories.

Yes, home or Point of Care tests are available either from pharmacies or by mail order. These usually only detect the drug groups (e.g. opiates) rather than the individual drugs such (e.g. morphine). They do not have the second confirmatory step which is required to eliminate false positive results and the quality of the measurement is generally inferior to that provided by an accredited laboratory. Home testing alone is not suitable where legal action might be considered.

A number of prescription drugs are related to amphetamine (pseudoephedrine, phentermine) and are available either over the counter or by prescription – these may give a positive screening result if present in sufficient quantities. The detection of these drugs is optional under AS/NZS 4308 – confirmatory laboratories will either detect them and report them by name, or not detect them. Other unrelated medications such as ranitidine, or naturally occurring substance such as tyramine, may also give false positive results that are excluded on confirmation.

Laboratories testing according to AS/NZS 4308 are required to test for the presence of creatinine to determine if the patient is overhydrated. Since each person excretes approximately the same total amount of creatinine in their urine each day, the urine creatinine level will be a measure of how concentrated or dilute their urine is and thus how much water they have been drinking. Drinking large amounts of fluids will dilute the urine and decrease the sensitivity of urine drug testing.

A patient's normal creatinine level varies greatly and is largely dependent on muscle mass and fluid intake. Small females with low muscle mass will excrete less creatinine in their urine than a large male. Drinking a significant amount of fluid in the preceding hour or two prior to sampling may result in a sample that is too dilute for testing and the laboratory will report it as unsatisfactory.

It is recommended that if patients have warning of the likelihood of testing, they manage their fluid intake by spreading it over an extended period, and avoiding caffeine (a diuretic).