Toxicology Update

2001, Volume 12, Number 1


Robert M. Johnson, Ph.D.
Patrick Ng, Ph.D.

It has been several years since the Warde Report focused on issues in forensic urine drug testing (FUDT). As in almost all disciplines, the complexity in FUDT has increased and the rate of change may accelerate. The major areas of change to date are in attempts to defeat the urine tests (e.g. adulteration) and in the availability of on-site screening test kits. In the future, we will almost certainly see a growth in the use of samples other than urine, such as hair, sweat, and saliva, which are less susceptibe to adulteration and may provide longer windows of detection. Changes in cutoffs for certain drugs like cocaine and amphetamine are also likely. As testing methods improve, lower cutoffs can be achieved. This results in fewer false negatives without risking false positives due to assay error. There are also some new drugs of concern, such as MDMA (Ecstasy) and at least one example of false positive possibilities caused by natural food consumption.

The FUDT industry tends to follow the Mandatory Guidelines promulgated by the Substance Abuse and Mental Health Services Administration (SAMHSA) for federal workplace drug testing programs. A new set of guidelines is in progress. Many of the changes in drugs and cutoffs seem certain to occur and are anticipated in the immediate future. Updates in meconium testing and comprehensive drug screen are also covered in this article.


Methods used to Defeat Urine Drug Tests

The consumption of excessive amounts of water is potentially effective because the amount of drug excreted by an individual is largely independent of water consumption. Since this excess water is quickly eliminated as urine volume, the drug concentration is less than it might have been, and potentially much less. Since testing is based on urine drug concentration and does not seek to measure amount excreted per unit time, this can be effective, but only if the donor has a relatively low body drug burden and does not dilute the urine below the creatinine cutoffs. Creatinine is spontaneously formed in muscle and excreted at a more-or-less constant rate. It then provides an “internal standard” to determine the “dilution status” of the sample. Samples with creatinine below 20 mg/dl and specific gravity less than 1.003 are defined as “DILUTE” by SAMHSA. Samples with a creatinine < 5 mg/dl and a specific gravity < 1.001 or > 1.020 are considered as “SUBSTITUTED”.

Adulterants are substances that are slipped into the urine at the time of collection and either interfere with the test methods or chemically destroy the target drug(s), usually marijuana metabolites (Table 1).

Table 1
Common Adulterants
Water (DILUTION)AllCreatinine, Specific Gravity
AmmoniaAllOdor, pH
BleachAll, esp. THCOdor
Glutaraldehyde (URINEAID)All, esp. THCBizarre data
Soap/DetergentAll, esp. THCBizarre data, foams, odor
Nitrite (KLEAR)THCSpecific Test
Chromate (URINE LUCK)THCSpecific Test
Peroxidase (STEALTH)THCTest under consideration
Comment: There are dipsticks available which allow for adulterant testing at the collection site. This has advantage of early detection of unstable adulterants like bleach and STEALTH which can degrade and are harder to detect in the lab.

The early adulterants like salt, ammonia, bleach, and glutaraldehyde were generally poor because they were ineffective and/or easy to detect. These are now rarely seen. They affect the immunoassays to give “bizarre” results. We use a dipstick to further prove their presence and issue a report suggesting an observed recollection. However, we are not able to report specific adulterants.

The more common adulterants are the oxidants. The major marijuana metabolite can be oxidized to a form that will not be detected by the GC/MS assay, even though the immunoassay screen may still give a positive result. Examples in this category are nitrite (KLEAR), chromate (URINE LUCK, pyridinium chlorochromate), and peroxidase (STEALTH). KLEAR is a white powder and URINE LUCK is a vial of orange liquid. STEALTH is sold as a package containing two vials, horseradish peroxidase powder and liquid hydrogen peroxide substrate. We are currently testing for nitrite and chromate using SAMHSA approved quantitative cutoffs. The assays are specific and quantitative and a repeat test is performed on a second aliquot if the adulterant screen is positive. We also use a dipstick which reacts with both nitrite and chromate, but produces different colors. Normal urine concentrations of these two compounds are far below those achieved with adulteration. The excess nitrite found in some urine specimens due to urinary tract infections, bacterial contamination or improper storage is also far below the SAMSHA cutoff. We will likely also test for STEALTH when a suitable test is available.

The oxidants are designed to defeat primarily the marijuana testing. In general, they do not affect the other drugs tested, although opiates may be masked if an acid is added with chromates. This effect is not seen at normal pH values.

Chromates (about 1 in 500 samples) are the most popular in our area. Nitrites are found in less than 0.1%. The fact that very few marijuana positive screens fail to confirm unless they have chromates or nitrites suggests presently STEALTH is not prevalent. It is possible, however, that the marijuana metabolites are not immunoassay reactive after oxidation by STEALTH.


Highlights of SAMHSA Revised Mandatory Guidelines (Draft #2)

The revised mandatory guidelines for federal workplace drug testing programs include many sweeping changes. It appears that point-of-collection (on-site) testing and screening-only laboratories will be allowed, both with extensive regulation just as with the current comprehensive laboratories. It also appears that testing of specimens other than urine (hair, saliva, and sweat) will be sanctioned, again with regulations, cutoffs, etc. just as with urine.

Presently Warde Laboratory has no immediate intentions of promoting on-site or offering alternate specimen testing. However, we will consider these options when the demand from our clients justifies our expansion in these directions.

Of more immediate interest are proposed changes in some urine cutoffs and drugs included (Table 2). For the cocaine metabolite, benzoylecgonine, the screen and confirmation cutoffs will be reduced to 150 and 100 ng/ml, respectively. For amphetamine and methamphetamine, they will be reduced to 500 and 250 ng/ml, respectively. For a positive methamphetamine, only 100 ng/ml of the metabolite amphetamine is required. The “amphetamines” assay must also include the designer drugs MDA, MDE, and MDMA (Ecstasy) with similar sensitivity.

Table 2
Cutoffs Proposed in SAMSHA Guideline Revision (Draft #2)
Urine, Current Screen (ng/ml)Urine, Proposed Screen (ng/ml)Hair Screen (pg/mg)Oral Fluid Screen (ng/ml)Sweat Screen (ng/2.5 ml)
Marijuana Metabolites50501.041.5
Cocaine Metabolites3001505002010
Opiate Metabolites200020002004010
The table illustrates the fact that drugs/metabolites are more concentrated in urine. Note the exceptionally low cutoff needed for screening hair for marijuana metabolites. 1 pg/mg is one part per billion by weight. Marijuana metabolites tend not to deposit in hair.

Warde laboratory has the technical capability to operate with these lower cutoffs and will make all these changes when the cutoff guidelines are finalized in the Federal Register.


Quantitative Reporting

Our reports include GC/MS quantitative concentrations for most positives. This is somewhat controversial in that these numbers can not convey much information and sometimes lead to misinterpretation, especially for the rapidly excreted drugs such as cocaine, opiate and amphetamine metabolites. Milligrams (mg) of drug are dosed and the test results are in nanograms (ng) per ml. One mg is one million ng and urine cocaine metabolite levels can reach 500,000 ng/ml without being “toxic”. The dilution with water can also modify the concentration by as much as 20-fold. So, for most drugs the numbers are highly variable. For marijuana (THC), the drug distributes to fatty tissue and is released over a longer period of time and urine concentrations are not so peaked. In THC reporting, the THC/creatinine ratio is also reported because a positive result is only truly high if the ratio is high (over 100 ng/mg). This drug/creatinine ratio should also be considered when determining a result for another drug is high or not. For the short-lived drugs, a high concentration and especially high ratio almost certainly indicates drug use within the last day or two. It should be emphasized that a positive urine drug test indicates recent drug use. In most cases, we only have one lab result and there are several variables such as the amount used, when used, how often, etc.; a positive test still can not tell if the person was under the influence at the time of collection. The drug/creatinine ratio is very useful in monitoring patients over a period of weeks or months in drug rehabilitation programs. The interpretation of patient compliance also depends on the frequency of testing. Contact Warde Laboratory if you have questions.


Possible Causes of Positives by Consumption of Natural Substances

Although this possibility is remote, it is not impossible. We encourage our clients to contact us if donors are adamant that they are innocent of illegal drug use.

Poppy Seed Ingestion
Although poppy seeds can give a positive morphine result even with the 2000 ng/ml cutoff, they will never produce a positive for the heroin metabolite, 6-acetylmorphine.

Hemp Seed Products
Products made from hemp seeds for human consumption include coffee, beer, lip balm, and hemp seed oil. Only the latter has toxicological significance. In one study, volunteers who consume 10 ml or more oil for several days have given urine samples that were confirmed positive for the THC acid metabolite that we routinely find in the urine of marijuana users. There is no marijuana effect from this amount of oil consumption. This is a plausible defense for a THC positive which might be occasionally used by donors and attorneys. Retesting after one week abstinence in hemp food products is an option.

Coca Tea
Five or more years ago, there was at least one positive cocaine case overturned based on the defense of drinking coca tea (Mate de Coca), made from the leaves of the coca plant. This tea was never widely used and has been barred from import for several years. It is not a current problem.

Herbal Teas
Individuals will occasionally claim that an herbal tea caused their positive THC results. To our knowledge, there is no basis for this claim. If a donor persists, we will test an unopened bag/box of the suspected tea.


Meconium Testing

All meconium samples are tested for cocaine metabolites, THC metabolites, and opiates using two different immunoassays (EMIT and KIMS) for each analyte. This is helpful in eliminating false positives and false negatives. For example, some samples contain a matrix interference which causes a positive interference with the KIMS technique but a negative interference with the EMIT technique. These samples are repeated with an additional step to remove the interference. Secondly, the antibody specificities of the two methods are somewhat different, and the metabolite mix in meconium is different from that in urine, so this approach gives better coverage in detecting drug presence.

Drug screen samples occasionally produce borderline results. Most of these have target drug present, but not enough to be clearly positive. With a single assay, one can enforce a rigid cutoff. This is what we do in forensic urine drug testing. Because we have two immunoassay results on meconium, the situation is not so simple. Samples occasionally are positive for a drug by one test, but slightly below the cutoff by the other. We regard these as clinical tests and feel that the patient is best served by calling these samples positive. A comment is added to the report indicating that it is an “equivocal” or “weak” positive.

Over 90% of positives are “strong”. It is not necessarily true that a “strong” positive indicates more drug exposure for the infant, although there could be such a correlation.

We re-emphasize that these tests are for medical use only. If custody decisions are to depend strongly on drug test results, one needs to have a GC/MS confirmed positive. This can be done on mother or newborn urine, or on meconium. “Weak positives”, especially for THC, may confirm negative even though drug metabolites are present. Newborn urine will also often give a false negative GC/MS THC confirmation, since newborns excrete different, unknown THC metabolites, compared to adults.

GC/MS confirmations must be ordered by contacting Warde Laboratory. We must have about 2 grams of meconium left, to do the confirmation. It is sent to an outside laboratory and will take about a week.

This communication should be shared with Risk Management and Social Services Departments.


Comprehensive Drug Screens

The urine (UDS) and serum (SDSC) comprehensive drug screens include a drug abuse screen and two or more chromatographic procedures to detect a wide variety of other drugs. A gas chromatographic (GC) procedure for volatiles is one of these. It detects ethanol, methanol, isopropanol, and acetone. The yield for the volatiles screen is exceptionally low, except for ethanol which is also detected in the drug abuse screen step. Also, the metabolic acidosis resulting from methanol and isopropanol ingestion enables the physician to order the volatile screen as needed.

As of 2/1/01, we no longer include the GC volatile screen as a routine part of the urine and serum comprehensive drug screens.

A second change that was recently implemented in comprehensive screen was the addition of GC/MS with intensive library searching to augment thin-layer chromatography.

If you have any question regarding forensic urine drug testing and meconium testing, please call Warde Medical Laboratories at 800-876-6522. Our Client Service and Toxicology staff will be glad to help you.



  1. Baer D, et al. Workplace drug testing: Two cautionary
  2. cases. MLO 1994; January: 26 -28.
  3. Cook J, et al. The characterization of human urine for specimen validity determination in workplace drug testing: a review.
  4. JAT 2000; 24: 579-588.
  5. Kunsman G, et al. The effect of consumption of Hempen Ale on urine cannabinoid screens. JAT 1999; 23: 563-564.
  6. Mandatory guidelines for federal workplace drug testing programs (Draft #2), SAMHSA, 2000.
  7. Paul B, et al. Effects of pyridinium chlorochromate adulterant (Urine Luck) on testing drugs of abuse and a method for
  8. quantitative detection of chromium (VI) in urine. JAT 2000; 24: 233-237.
  9. Urry F, et al. Nitrite adulteration of workplace urine drug-testing specimens I. Sources and associated concentrations of
  10. nitrite in urine and distinction between natural sources and adulteration. JAT 1998; 22: 89-95.
  11. Wu A, et al. Adulteration of urine by "Urine Luck". Clin Chem 1999; 45:1051-1057.