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SAMPLING

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  366

2026-08-12

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SAMPLING

The typical sample used for workplace drug testing is urine. The vast majority of commonly abused drugs will ultimately end up in urine with which they are excreted. Typically, the subject will go to a clinic or doctor’s office to give a urine sample. Often, this is part of a general physical exam. In many clinics this is an unsupervised process that can lead to deliberate attempts to alter the sample. Sometimes a subject will dilute the urine with water from the commode or sink in the hopes that the drug will be so dilute that it will not be detected or will fall below the cut-off level for that drug. There have also been cases where subjects smuggle drug-free urine into the clinic and substitute it for their own. Some laboratories will try and prevent these activities by having a witness present when the sample is given. Others will put bluing agent in the commode and turn off the water in the sink. The laboratory will also have the collector immediately take the temperature of the urine. This will uncover attempts to dilute the sample with room temperature water. Some protocols call for determining the specific gravity of the urine sample. This is higher than that of water, so dilution of the urine will result in a decrease in the specific gravity. In some cases, workers have complained that they were not informed that their physical examination included a drug screening test. Another problem that occurs in clinical laboratories is mixing up samples. Some laboratories generate a high volume of workplace drug samples and if proper labeling and chain of custody procedures are not followed, then it is pos sible for samples to get mixed up. Likewise, if the testing laboratory and/or the courier don’t use proper chain of custody techniques, the samples could once again be mixed up. This problem can be exacerbated if multiple laboratories are used. For example, a subject may go to a medical laboratory to give a sample. This may then be screened at a different laboratory and then confirmed at a third laboratory. All of these transfers and handling increases the chances that an accidental mix up will occur.