Urine Testing for Recreational Drugs - 5 Useful Tips

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Recreational drugs may be implicated in, or complicate analysis of, diverse clinical presentations. Urine toxicology tests are useful in the detection of these harmful agents.

In terms of drugs of abuse, urine toxicology screens will test for the presence of the five major classes of these substances; amphetamines, cannabis, cocaine, opioids and phencyclidine (PCP). You must exercise caution in the interpretation of the results of these tests as they have several limitations. Importantly,

1) A positive test does not necessarily equate to acute ingestion. Many of these tests remain positive for days or even weeks after ingestion of the substance in question. It is often difficult, therefore, to relate the timing of symptoms to the time of ingestion.

2) A positive test does not necessarily equate to cause of disease. Ingestion of drugs may be incidental to the clinical presentation. So, for example, a person may present with chest pain and a positive urine test for cocaine ingestion. We cannot assume that the chest pain is due to cocaine, it is just one possibility and we must consider all other possibilities pertinent to the case.

3) Some commonly used medicinal drugs may result in false positive results on a urine tox screen. This is particularly true for the detection of the marijuana breakdown product THC. It also makes the interpretation of a positive result for amphetamines difficult. Many legal drugs can produce a false positive for the latter agents. The best way of approaching this problem is by making a detailed record of medicinal drug use (taking a detailed drug history) and, if the result is of critical importance, cross reference the medicinal drugs with the test result to see if there are reports of false positives. Urine toxicology must be interpreted in the context of a detailed drug history.

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4) False negative results are not uncommon. The tests are not foolproof in detecting some drugs of abuse. If intake of a specific agent is strongly suspected and important to establish, chromatographic tests may be requested for that specific agent (specific drugs). An example of the later would include ingestion of MDMA. This compound is poorly detected on urine testing but will be picked up by chromatographic analysis.

5) These tests cannot distinguish between use of legal versus illegal opioids, for example codeine versus heroin. Both are detected by the presence of opioid metabolites in the urine.

 Amphetamines

 

 Duration

  • 2 days

 Problems with Test

  • Cross reaction with legal drugs and remedies (false positives)
  • Poor pickup of MDMA abuse

 Cannabis (THC metabolites)

 

 Duration

  • Depends on usage level
  • Single use: 3 days
  • Repeated use: 2 weeks

 Problems with Test

  • Cross reaction with legal drugs (false positives)
  • Be very careful before accusing a little old lady on antidepressants of abusing marijuana!

 Cocaine

 

 Duration

  • 2 to 4 days

 Problems with Test

  • Reliable
  • Urine toxicology screen for cocaine is generally considered to be very reliable and as the abuse of this agent is increasingly responsible for presentations to ER/ED, this test is useful. Cocaine may be detected on urine testing within one hour of ingestion. The test may remain positive for days in habitual abusers.

 Opioids - natural (eg codeine)

 

 Duration

  • 2 days

 Problems with Test

  • Does not distinguish legal and illegal opioids
  • Some cross-reactivity with other agents (false positives)

 Opioids - semisynthetic (eg heroin)

 

 Duration

  • 2 days

 Problems with Test

  • Does not distinguish legal and illegal opioids
  • Some cross-reactivity with other agents (false positives)

 Opioids - synthetic (eg methadone)

 

 Duration

  • 3 days

 Problems with Test

  • Does not distinguish legal and illegal opioids
  • Some cross-reactivity with other agents (false positives)

 Phencyclidine (PCP)

 

 Duration

  • 8 days

 Problems with Test

  • Cross reactivity with legal drugs (false positives)

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