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Oral fluid

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  313

2026-10-27

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Oral fluid

Saliva, or oral fluid (as it is more correctly known), is a plasma ultrafiltrate produced through the parotid and other glands in the oral cavity. Many drugs, including alcohol, that are present in the blood therefore also appear in the saliva. Oral fluid can, however, be subject to contamination from recent oral intake of drugs and alcohol, or simply from retaining these in the mouth and expelling them without ingestion. Contamination can last for some time, depending on the drug’s lipophilicity and water solubility. Alcohol, for example, is generally dissipated from the mouth by absorption and exhalation within 15 min. A 15–20 min waiting period is therefore standard in an evidential breath-testing environment, prior to the subject being offered an evidential breath test, and a similar waiting period is essential for a test of salivary alcohol. A number of vendors sell salivary alcohol test strips, based on the principle of enzymatic oxidation. These are used most appropriately as screening devices, since their quantitative accuracy is highly operator-dependent. They are, however, often sold directly to the public for self-testing, and it is possible that people may make inappropriate decisions about driving based on an inaccurate test, and may ignore the legal prohibition against driving while affected, irrespective of BAC. There is, however, a good correlation between circulating blood alcohol and saliva alcohol and, if for some reason a blood or breath sample cannot be provided, a properly collected and preserved oral fluid sample can be subjected to a gas chromatographic analysis with the appropriate forensic safeguards. For these purposes, oral fluid should be collected in a tube with minimal headspace to prevent loss and an enzyme inhibitor to inhibit post-collection alcohol production.