NDARC Technical Report No. 120 (2001)
EEXUTIVE SUMMARY
This paper provides a detailed review of drug testing procedures, focusing on the most commonly abused classes of drugs. Four biological specimens that can provide information about human drug exposure are covered. These include urine, hair, saliva and sweat. An overview of the physiology of each matrix and mechanisms of drug incorporation is included followed by a discussion of issues related to their collection, analysis and interpretation. Conclusions regarding the advantages, disadvantages, applicability and usefulness of each matrix for drug detection are provided.
The biological detection of drug use is a two-step process. It involves a screening test which, if found to be positive, is followed by a confirmatory test. There are two primary methods of analyzing specimens for drugs: immunoassay and chromatography. Immunoassay is typically used to screen for drugs, as it is quick and comparatively inexpensive. The main limitations of immunoassay screens are low specificity and high cross-reactivity resulting in relatively high rates of false-positive test results. A confirmatory test is conducted to guard against this using a different analytical technique of equal or greater sensitivity. Chromatographic tests such as gas chromatography separation coupled with mass spectrometry detection (GC/MS) are recommended.
It is important to note that the determination of drug use through biological analysis is never absolute. Numerous factors associated with the person tested (e.g. metabolism), the drug used (e.g. pharmacokenetic properties, route of administration), the sample taken (e.g. window of detection, biology of drug incorporation), the collection procedure (e.g. testing schedule) and the analytical procedure (e.g. limit of detection, cross-reactivity) all affect the results obtained. Consequently, there are four possible outcomes of a drug test which must be considered: (i) a true-positive result, where a tests correctly identifies the presence of a drug; (ii) a false-positive result, when a drug is detected by a test when, in fact, that drug is not present in the sample; (iii) a true-negative result, where a tests correctly identifies the absence of a drug; and (iv) a false-negative result, when no drug is detected by a test when, in fact, a drug is present in the sample. There is also much information associated with drug use that cannot be determined by biological analysis. For example, conclusions regarding current intoxication, quantity of drug used, frequency of use, and physical or psychological dependency cannot be made.
Drug use determination is undertaken through the analysis of a drug’s metabolites as well as the drug itself depending on the sample being examined. This is important for two reasons. Firstly, metabolite(s) are most likely to be detected in some samples, primarily urine, as they often have a longer half-life than the parent compound (drug consumed). Secondly, identification of relative metabolite concentrations is often necessary to determine the drug that has been consumed. Different drugs can metabolise into the same compounds, or an unmetabolised drug may be present in a sample because of passive contamination rather than consumption (as has been shown with hair).
Drug use is currently assessed in urine, hair, saliva and sweat. Each biological sample has its own unique advantages and disadvantages stemming from its inherent properties and our current state of knowledge. A summary of these issues can be found in Table 4.
Urine is the most widely used matrix. In Australia, analytical facilities and procedures for urinalysis are well established, relatively convenient and competitively priced. Urine offers only an intermediate window of detection (1-3 days) thus making test scheduling a significant issue for many applications. Its susceptibility to tampering and adulteration is also a problem and makes appropriate supervision critical.
Hair analysis offers the largest window of detection (7-100+ days) and can provide information on historical drug use spanning up to several months. Much research has been undertaken examining hair testing, however incomplete understanding of the mechanisms of drug incorporation has made straightforward result interpretation difficult. The interest in this technology, stemming from its broad range of potential applications, is likely to result in further improvements in the reliability and validity of hair as an alternative test matrix to urine.
Saliva analysis is also a developing technology. Currently, there are limited analytical facilities in Australia, however, established United States laboratories are accessible. Sample collection is relatively quick, noninvasive and resistant to tampering although as with urinalysis, adequate supervision is required. Saliva analysis has been shown to be useful in determining very recent drug use (1-36 hours). It is not considered economically viable or practical for continuous drug use monitoring.
The analysis of sweat may prove to be the matrix of choice for the medium-term, continuous monitoring of drug use due to recent developments in sweat patch technology. However more naturalistic trials are required. It may also offer an economical alternative to urine, as comparable results can be obtained with fewer analyses. Analytical facilities and expertise is still lacking in Australia but progress is being made.
Drug testing has become a faster, more convenient process with the development of point-of-collection (on-site) drug testing devices. This paper concludes with a review of some of the many commercial on-site devices used to screen for drugs of abuse in urine, sweat and saliva. Although improvements are being made, only on-site urine tests are considered adequate at this time. Manufactured devices for the collection of saliva and sweat samples that are analysed by accredited laboratories are reviewed. A test device for the detection of irregularities in urine, and hence possible adulteration, is also reviewed.