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Interpretation of adulterated and substituted specimens

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  p149-150

2026-10-04

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Interpretation of adulterated and substituted specimens

It is not uncommon for persons being tested to try to adulterate their sample in some way. This may be by substituting an alternative specimen or by addition of substances that will interfere in some way with analysis of the sample, that will change the nature of the sample such that it is not detected, or that dilutes the sample, thereby reducing the concentration of the drug.

Nearly all the adulterants that are used today to oxidise THCA are classified in the recently issued HHS Guidelines as exogenous substances not expected to be present in urine. One exception to this is nitrite, which can occur in urine as a result of bacterial infection, the ingestion of certain foodstuffs and the use of some medica tions. In one study (Urry et al. 1998) that considered these sources and the presence of nitrite in normal urine, the highest urinary concentration was approximately 130 lg/mL; the cut-off used today is 500 lg/mL, almost four times this concentration. Some of the other adulterants include chromium (VI), peroxide, iodine and bleach; none of these should be detected as a result of normal physiology and metabolism. However, a donor may claim that their presence is the result of workplace exposure or the ingestion of vitamins or herbal material, and the person interpreting the results needs to be prepared to refute these claims. The interpretation of substituted specimens has already caused discussion; some investigators believe that the criteria of less than 5 mg/dL creatinine and less than 1.002 relative density are too high for some individuals and some occupations. To date they have produced no data to support this belief. Before establishing the  criteria, HHS performed an extensive literature review on what might be expected to be normal ranges for creatinine and relative density in both healthy individuals and those with certain diseases that may lead to polyuria (Cook et al. 2000). Following this review, it was decided that the criteria of creatinine less than 5 mg/dL and a relative density of less than 1.002 or greater than 1.020 were sound ones for establishing a specimen as substituted. Recently, Barbanel et al. (2002) reviewed over 800 000 urine specimens. In this population both creatinine and relative density measurements were taken from over 13 000 specimens, and none of these satisfied the criteria for a substituted specimen. These authors also examined the medical records of patients who satisfied one of the criteria and reported that these were either neonatal, moribund or so severely ill that essentially none could have been in the working population. Further information has been provided by a study in which 12 volunteers (5 men and 7 women) consumed 2.5 L of water over a 6-hour period and urine specimens were collected for the measurement of creatinine and specific gravity; none of the 500 specimens collected was identified as substituted using the criteria (Edgell et al. 2002). In 2003 the Federal Aviation Authority sponsored a symposium to investigate whether ‘substituted’ specimens can be produced under normal conditions. It was reported that certain individuals had been shown to excrete urine with a creatinine of less than 5 mg/dL. This observation resulted in the differences in the procedures used to test federal employees and those covered under the DOT requirements.