aIn Europe and places where testing for PCP is not of interest, benzodiazepines (BZO) test with a cut-off concentration of 5 ng/mL is substituted for PCP.
The collection pad is made of polymeric material chosen for its rigidity under wet conditions and good liquid flow. Size of the collection pad is optimized to collect the minimal oral-fluid volume to accomplish the testing and confirmation processes so that the time required to complete these procedures can be reduced to 5 to 8 min. It is estimated that the total sample volume col lected by the pad is 0.55 mL. About 0.3 mL will be used to complete the screen testing, and this will leave 0.25 mL for confirmation testing.
Because of the sensitivity requirement of the tests, the chemistries of the test strips originally designed for urine testing have to be modified to allow for the lower C.O. detection limits. Furthermore, because THC residue in oral fluid is even more absorptive ("sticky") to polymeric surfaces than its carboxylic acid metabolite in urine, the choice of buffers and surfactants to be used requires extensive studies. Evaluations of the currently commercially available antibodies showed that all of them are designed for the carboxyl derivative and do not have high affinity toward THC. Hence, a compromise on the sensitivity of THC test has to be made.
The Oratect test is based on the principle of competitive immunoassay, in which drug derivatives immobilized on a lateral-flow membrane compete with the drugs that may be present in oral fluids for limited antibody binding sites on colored colloidal gold antibody conjugates. In the absence of drugs in the oral fluids, the colloidal gold antibody conjugates will bind to the drug derivatives on the membrane and form red colored lines indicating negative results. Conversely, drugs present in the oral-fluid samples will bind to the colloidal fluid antibody conj ugates and prevent them from binding to the drug derivatives on the membrane. Hence, the absence of a colored line at a specific test region indicates a positive result for that particular test.
The Oratect is noninstrumental, with all necessary reagents incorporated into the one-piece device (Fig. 1). To run the test, rub the collection pad in a circular motion inside both cheeks and on top of and beneath the tongue until gold conjugate appears in the window. Cap the pad and check for the presence of line within 5 min. If the screening test indicates a positive result, the collection pad can be sent to a laboratory for gas chromatography (GC)-mass spectrometry (MS) confirmation analysis of the drugs retained in the collection pad. This is accomplished by pinching of the collection pad with the cap to detach it from the test device. The pad is stored in a buffered vial to be sent to the laboratory.
The collection procedure serves several functions. Moving the device inside the mouth cavity may stimulate oral-fluid production. Moreover, it is believed that THC residues are most abundant inside the mouth cavity around the inside of cheek. A circular motion may be the best way to recover these residues.
To ensure that the test results are readable within 3 to 5 min, the line intensities of positive and negative results have to remain differentiable over a period of 2 to 5 min. Results of a study shown in Fig. 2 demonstrate substantial color line intensity differentiation between positive and negative results for amphetamine (AMP) and cocaine (COC) tests, while the color for the control line did not change. It also shows there was little variance from 2 to 5 min. Similar results were obtained for the THC, methamphetamine (MET), opiates (OPI), and phencyclidine (PCP) tests.
The precision of the Oratect device was evaluated using pooled negative oral fluids spiked with various concentrations of the seven drugs. Twenty samples were run for each concentration. The results obtained are shown in Table 2.
3. Correlation With Other Assays
3.1. Correlation With Enzyme-Linked Immunosorbent Assay
In a report comparing oral-fluid enzyme-linked immunosorbent assay (ELISA) (Immunalysis Corporation, Pomona, CA) with Oratect (6), aliquots of pooled negative oral fluids were spiked with five drugs (COC, OPI, AMP, MET, and PCP), and the drug concentrations in these aliquots were assayed by both tests. All together, 26 serial dilutions at concentrations ranging from 600% (6X) to 0% (0X) of the C.O. concentrations were tested in duplicates by Oratect and ELISA. Results are summarized in Table 3. It shows that all samples spiked at 1.5X C.O. concentrations and above were determined to be positive by both ELISA and Oratect. All samples spiked at or below 0.7X C.O. concentrations gave negative results on both assays.
3.2. Correlation With Urine Drug Screen and Confirmation by GC-MS
A total of 465 volunteer subjects at a drug rehabilitation program were tested with both urine drug screens and the Oratect device. In this experiment, urine specimens were collected under observed conditions and screened for five drugs using Monitect® PC11 drug screen (Branan Medical Corporation). The Oratect tests were performed immediately after the subject exited the restroom. Results from the two test methods were compared only at the end of the day. The collection pads from the positive Oratect test devices were sent for GC-MS confirmation tests at Scientific Testing Lab (Richmond, VA). The
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