Drug Testing Basics

1.  DRUGS DETECTED AND DETECTION PERIODS

2. "BEATING THE TESTS:" ADULTERATION, ETC.

3. EASE OF USE

4. ACCURACY AND RELIABILITY

5. KNOWN PROBLEMS

6. "FALSE POSITIVES" AND "FALSE NEGATIVES"

7. ACADEMIC STUDIES

1. DRUGS DETECTED AND DETECTION PERIODS

Many factors influence the length of time required for drugs to be metabolized and excreted in the urine. The most important of these is the half-life of the drug. Half-life refers to the length of time the body requires to reduce the amount of a given drug in the blood by one-half. In addition to half-life, the length of time drug metabolites are present in urine is influenced by each individual's rate and efficiency of urine production, pH, fluid consumption patterns, the amount of drug taken and the length of time over which drug was consumed. Ingesting a large volume of liquid or using diuretics may "dilute" the drug in a larger amount of urine, making drug detection more difficult. The larger the dose of drug consumed and the more frequently drugs are consumed, the longer the time required to reduce the level of drug in the urine to a point where it will no longer be detected. For all these reasons the detection periods given are estimates only.

METHOD	DRUG	Maximum Detection Period (after last use)
Urine (detection begins four to eight hours after use)	Marijuana and Hashish (THC)	4 days to six weeks, depending on frequency and intensity of use
	Opiates (heroin, opium. morphine, codeine, etc.	4 days
	Cocaine (including "Crack")	3 days
	Amphetamine ("Speed")	5 days
	Methamphetamine ("Crank," "Ice" "Ecstacy")	5 days
	PCP ("angel dust")	10 days
Oral Fluid / Saliva (Detection begins immediately upon use)	Marijuana and Hashish (THC)	8 to 12 hours
	Opiates (heroin, opium. morphine, codeine, etc.	2 to 3 days
	Cocaine (including crack)	2 to 3 days
	Methamphetamine ("Crank," "Ice")	2 to 3 days
	Ecstasy	2 to 3 days
Hair (Detection begins 3 days after use)	Marijuana and Hashish (THC)	Up to 90 days
	Opiates (heroin, opium. morphine, codeine, etc.	90 days
	Cocaine (including crack)	90 days
	Amphetamine (Speed")	90 days
	Methamphetamine ("Crank," "Ice" and Ecstasy)	90 days
	PCP ("angel dust")	90 days
	Ecstacy (MDMA)	90 days

2. "BEATING THE TESTS:" ADULTERATION, ETC.

Urine	Super-hydration: drinking large quantities of water prior to test
	Substitution: submitting a different person's urine as the sample
	Dilution: adding water directly to urine sample
	Catheterization: using a catheter to put another person's urine in the bladder, and voiding it out as a sample (a variant on substitution)
Oral Fluids / Saliva	None known
Hair	Very difficult: repeated bleaching of hair may reduce detectable drug metabolites

3. EASE OF USE

Urine Note: Many test administrators do not like potential exposure to urine when using test kits. Test subjects often feel urine testing is intrusive	Training required: moderate
	Observation: direct observation is desirable, supervision is required
	Test area: toilet area must be prepared
Oral Fluid / Saliva Note: Test administrator typically find oral fluid tests easy and clean to administer. Test subjects usually feel minimal level of intrusion with oral fluid tests	Forms and Procedures: extensive chain of custody forms and procedures
	Training required: very little
	Observation: direct observation is simple and non-intrusive
	Test area: no special requirements
	Forms and procedures: very simple
Hair Note: Test administrators typically find hair testing clean and easy to administer. Test subjects usually feel minimal level of intrusion, but some object to the long window of detection (90 days)	Training required: very little
	Observation: direct observation is simple and non-intrusive
	Test area: No special requirements
	Forms and procedures: Very simple

4. ACCURACY AND RELIABILITY

Urine	99% accurate with GC/MS confirmation of all apparent positives and MRO review. This should always be done to assure the accuracy of positive results. On-site screening kits are 95 to 99% accurate at the time of initial screen
Oral Fluids / Saliva	99% accurate with GC/MS confirmation of all apparent positives and MRO review. On-site screening kits are 93 to 97% accurate at the time of initial screen
Hair	99+% accurate. All apparent positives are routinely subject to GC/MS confirmation, and MRO review

5. KNOWN PROBLEMS

Urine	Dietary poppy seeds may screen positive as an opiate, requiring GC/MS confirmation. Marijuana may screen positive for up to six weeks after cessation of heavy use.  Certain over the counter medications may screen positive for amphetamine, requiring GC/MS confirmation.
Oral Fluids / Saliva	Marijuana screens positive for only 4 to 16 hours after last use. Even within that time period, small amounts may not be detectable.
Hair	There has been some concern over reports that darker hair retains drug metabolites for a longer period than lighter hair. A recent peer-reviewed article provides evidence that all hair retains drug metabolites to the same extent. See Kelly, Mieckowski, Sweeney, and Borland, Hair analysis for drugs of abuse in Forensic Science International, 107 (2000) 63-86. Marijuana is more difficult to detect than are the other drugs.

6. "FALSE POSITIVES" AND "FALSE NEGATIVES"

The accuracy rate of all screening tests is related to  the nature of the population being tested, cross reactions to legal substances, including various medications and foods, and the sensitivity of the test. These tests are called "screens" because they are designed to screen out all negatives, with positives being regarded as "presumptive positives" until Gas Chromatography / Mass Spectrometry confirmation.

False positive urine screens most often occur due to cross reactivity. For example, amphetamine positives on initial screens are often due to over-the-counter medications rather than illicit drugs. Similarly, urine screens will pick up on dietary poppy seeds as a "positive" for opiates, requiring a more sophisticated test (Gas Chromatography / Mass Spectrometry) to accurately determine if an illegal opiate drug metabolite is present.  

"False positives" may also occur because a screening test detects a substance that is slightly below the Federal cut-off level for the particular drug.  This is not a true "false positive' since the drug is present, but it is a false positive from a regulatory, and usually from a legal point of view.

"False negatives" occur when a screening test in insufficiently sensitive.  This most often occur when a drug is present at a level only slightly above the Federal cut-off level.

7. ACADEMIC STUDIES

Studies to look at:

1.   Federal:

An Evaluation of Non-Instrumented Drug Test Devices (click on title to view full article)

2. An Evaluation of Non-Instrumented Drug Test Devices, SUMMARY REPORT FOR WORKPLACE PROGRAMS and Recommendations for Purchasing NIDT Devices, Robert E. Willette, Ph.D., Duo Research Inc., under contract with the Administrative Office of the U.S. Courts (A.O.C.) Available from Orion Diagnostics, PO Box 218, Somerset, NJ 08875, Phone: (732) 246-3366. We hope to gain permission to post this study.

Summary: "The evaluation of the 15 devices was conducted with a majority of the specimens grouped around the screening cutoffs. It was found, as expected, that many devices gave a fair number of false positive and false negative results. It is also expected, based on experience in the field, that specimens encountered in most criminal justice and work-place testing situations will have fewer specimens with drug concentrations near the cutoff. This means that a much higher percentage of confirmed positive results and fewer false negative results would likely occur during actual testing in most situations."

3.   Peer reviewed journal:

Accuracy of Five On-Site Immunoassay Drugs-of-Abuse Testing Devices  E. Howard Taylor, Ernest H. Oertli, Jana W. Wolfgang, and Eric Mueller, Journal of Analytical Toxicology, Volume 23, Number 2, March/April 1999, pp.119-124.

Summary: The authors reviewed five commercially available products (PharmScreen™, Roche TestCup®, Accusign™ DOA 2, Status DS™, and American Bio Medica-Rapid Drug Screen).  The products were tested using known quality-control urine specimens, and with known positive and negative donor specimens previously analyzed by immunoassay and gas chromatography–mass spectrometry. The authors found that all these tests have a margin of error, and that claims for total accuracy were exaggerated.  Particular problems with screening for amphetamines were noted. 

We will be adding more articles shortly.   If you have one to suggest, let us know.