Oral Fluid

The terms oral fluid and saliva have been used interchangeably in the literature. However, oral fluid is a preferred term as it is the fluid that is collected and analyzed. It contains saliva (secretion of salivary glands), mucosal transudate and crevicular fluid.

Oral fluid is becoming a popular specimen for drug of abuse testing. The use of oral fluid in impaired subjects is of particular interest because it is easy to collect on-site as compared to blood and urine and provides a better indication of recent drug use. In forensic situations, it can be collected under close supervision to avoid adulteration and substitution. Concentrations of drugs in oral fluid correlate better with blood concentrations as compared to urine.

Collection of oral fluid is not very well standardized, and there are various techniques for its collection. In direct non-stimulated technique, there is more froth than actual liquid resulting in viscous and small sample size and causing problems in sample analysis. For this reason, many investigators suggest salivation stimulation by sour candy or citric acid crystals. Manual stimulation can be achieved by chewing on inert material such as Teflon. Substances such as Parafilm should be avoided as they may absorb lipophilic drugs. Various devices including Salivette, Omni-Sal, Intercept, Accu-sorb, Saliva Sampler and SalivaSac are commercially available for oral fluid collection. Samples collected using collection devices generally provide cleaner specimens as compared to direct spitting in which the sample contains cell debris, food particles and strings of mucous.

Once the oral fluid is collected, screening and confirmation are generally performed in the laboratory. Screening generally involves immunoassays, and confirmation is performed by GC-MS or LC-MS. In recent years, point of care devices have become available. These devices include OralLab, RapiScan, Drugwipe and SalivaScreen. Walsh et al. (55) compared these on-site devices and concluded that these devices perform well for the detection of methamphetamine and opiates, but poor for the detection of cannabinoids. The ability to accurately and reliably detect cocaine and amphetamine was dependent on the individual device (55). SAMHSA-proposed screening and confirmation cutoff values in oral fluid for various drugs of abuse are shown in Tables 4 and 5 (3).

Using a large number of oral fluid specimens (n = 77,218), one study investigated the rate of positivity for amphetamines, cannabinoids, cocaine, opiates and PCP in non-regulated workplace drug testing programs (56). The oral fluid samples were collected using Intercept Oral Collection device (OraSure Technologies, Bethlehem, PA). The device consists of an absorbent cotton fiber pad on which sample is collected by placing the pad between the lower gum and cheek for 2-5 min. The collected sample was placed in preservative solution for transportation to the laboratory. The samples were screened by EIA using cutoffs of 3, 15, 30, 3 and 120ng/mL for THC (parent drug and metabolite), cocaine metabolites, opiate metabolites, PCP and amphetamines, respectively. The positive samples were confirmed by GC-MS-MS using cutoffs of 1.5, 6, 30, 30, 3, 1.5, 120 and 120ng/mL for THC (parent drug), benzoylecgonine, morphine, codeine, 6-acetylmorphine, PCP, amphetamine and methamphetamine, respectively. Of 77,218 samples tested, 3908 (5.06%) confirmed positive. The frequency of positivity was THC (3.22%) > cocaine (1.12%) > amphetamines (0.47%) > opiates (0.23%) > PCP (0.03). In this study, the overall prevalence rate for drug detection was comparable to the urine drug prevalence rates in the general workforce (n > 5,200, 000, positive rate of 4.46%). Oral fluid positivity rates, for amphetamine and cocaine, were 60% higher as compared to urine suggesting that these drugs are more efficiently accumulated in oral fluid as compared to urine. Another remarkable finding in this study was

Table 4

SAMHSA-Proposed Initial Cut-off Concentrations for Oral Fluid Samples

Table 4

SAMHSA-Proposed Initial Cut-off Concentrations for Oral Fluid Samples

Analyte

Concentration (ng/mL)

THC parent drug

4

and metabolite

Cocaine metabolites

20

Opiate Metabolitesa

40

Phencyclidine

10

Amphetaminesb

50

MDMA

50

MDMA, methylenedioxymethamphetamine; SAMHSA, Substance Abuse Mental and Health Services Administration; THC, A9-tetrahydrocannabinol a Labs are permitted to initially test all specimens for 6-acetylmorphine using a 4 ng/mL cut-off. b Methamphetamine is the target analyte.

Table 5

SAMHSA-Proposed Confirmatory Cut-off Concentrations for Oral Fluid Samples

Analyte Concentration (ng/mL)

Table 5

SAMHSA-Proposed Confirmatory Cut-off Concentrations for Oral Fluid Samples

THC parent drug

2

Cocaine3

8

Opiates

Morphine

40

Codeine

40

6-Acetylmorphine

4

Phencyclidine

10

Amphetamines:

Amphetamine

50

Methamphetamineb

50

MDMA

50

MDA

50

MDEA

50

MDA, methylenedioxyamphetamine; MDEA, 3,4-methylene-dioxyethylamphetamine; MDMA, methylenedioxymethamphetamine; SHMHSA, Substance Abuse Mental and Health Services Administration; THC, A9-tetratydeocannabiol. a Cocaine or benzoylecgonine.

b Specimen must also contain amphetamine at a concentration great than or equal to the limit of detection.

the presence of 6-acetylmorphine in 66.7% morphine-positive samples. However, in another study using 114 adult arrestees, for THC, saliva had sensitivity of only 5% when urinalysis was used as the reference standard. Cocaine and heroin had sensitivity of 100 and 88% and specificity of 99% and 100%, respectively (57).

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