Introduction to Oral Fluid Testing

Addiction Professional, September 2004 | Go to article overview

Introduction to Oral Fluid Testing


What is oral fluid?

Oral fluid is a combination of saliva, gingival crevicular fluid (mucosal transudate), and small amounts of other components. The sources of saliva are the parotid, submandibular, and sublingual glands. The saliva produced by each of these glands differs slightly in chemical properties. At any given time, under typical conditions, there is about 0.5 ml of saliva in the mouth. Mucosal transudate is essentially a plasma filtrate that originates in the crevice between the gum and the teeth. Mucosal transudate contributes a small volume to the overall volume of fluid that is collected in the mouth. Collectively, all of these fluids, as well as other components, in the oral cavity combine to become "oral fluid."

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How do drugs get into oral fluid?

The oral cavity has a very dense capillary bed that makes it ideal for monitoring drugs circulating in the blood. Almost anything we absorb into our body ultimately appears in oral fluid. Testing oral fluid gives you an internal picture, a window, into what's happening in the body. Drugs get into oral fluid primarily by passive diffusion from blood. The physical and chemical properties of the drug determine to a large extent how much drug gets into oral fluid. Drugs that are highly bound to proteins in blood are inhibited from entering saliva and being deposited in oral fluid. Consequently, only the free fraction of drug that is circulating in blood can cross biological membranes and be found in oral fluid. Drugs that are highly protein bound in blood, such as THC, are inhibited from entering saliva.

The effect of pH on drug excretion in saliva is critical for basic drugs. The pH of blood is always at about 7.4, with minimal variation, whereas oral fluid pH ranges from as low as 5 to as high as 7.5. Therefore, except under highly stimulated conditions, saliva is acidic and blood is basic. If you have acid conditions on one side of a membrane and basic conditions on another, a basic drug will flow toward the acid side and become concentrated. For this reason, basic drugs tend to be more highly concentrated in oral fluid than in blood. Frequently, when we measure both oral fluid and blood, we see a higher concentration of drug in oral fluid. This is advantageous in terms of detecting drugs in oral fluid because most drugs are bases (THC being the notable exception).

How does marijuana get into oral fluid?

Marijuana is a distinctly different compound. THC, the active component of marijuana, is rapidly absorbed and is distributed throughout the body. There is very little evidence at this stage that THC in blood returns to oral fluid once it is absorbed into the bloodstream. So why do we find THC in oral fluid? During marijuana use (smoking and oral ingestions) THC is deposited in the oral cavity. This highly lipid soluble substance becomes bound to the membranes and the tissues in the oral cavity. A portion of the THC depot is ultimately absorbed into the bloodstream via transmucosal absorption. In addition. THC leaches out of the depot into oral fluid and can be detected for a number of hours after marijuana use.

Which drugs can oral fluid testing detect?

Essentially any drug that can be detected in blood or urine can also be detected in oral fluid. The Intercept[R] Oral Specimen Collection Device has been FDA approved for testing for the NIDA-5 drug panel (marijuana, cocaine, opiates, PCP, and amphetamines) as well as barbiturates, benzodiazepines, methadone, and methamphetamine (including ecstasy).

How is oral fluid drug testing done?

Oral fluid samples can be collected anytime, anywhere, without the need for special collection facilities. The collection process can take place in a small conference room or in an office rather than in a restroom. The donor must be observed to have nothing in his or her mouth for at least 10 minutes prior to the test. …

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