Onsite Testing

Onsite site is also referred to as point-of-care testing or point-of-collection testing (POCT). There has been much recent interest in the utility of rapid, easy-to-use urine drug testing devices in a variety of settings: emergency departments, drug treatment clinics, workplace drug testing, criminal justice, and enforcement of traffic laws. The major advantage of POCT is the reduction in turnaround time; shipping of specimens to centralized laboratories for testing is time-consuming and costly. Performing analysis at the site of collection and having results available without delay greatly increase the impact of test results. POCT testing provides (a) in the ED, rapid implementation of therapeutic intervention; (b) in drug treatment clinics, particularly if done in the presence of patients who tested positive, a powerful tool in deterring denial of drug use; (c) in the workplace, permits rapid hiring decision or deployment of workers in fitness for duty programs (49).

POCT devices require no sophisticated instrumentation or a permanent laboratory. Urine testing devices in single- and multi-analyte configurations come in different formats, such as a dipstick, a test strip enclosed in a cassette, and a cup where the specimen is collected into a cup containing a test strip (50). These devices are generally easy to use and rapid, with results usually available within a few minutes. Numerous devices for saliva testing are available and a few have been evaluated (10).

The most common of the devices utilize immunochromatography (also described as lateral flow immunoassay) where a drug in urine migrates along a porous membrane and inhibits a drug-antibody capture on the membrane. The designs of many of the commercially available test kits are based on variations of this basic concept. In one version, for example, drug molecules in a urine specimen and drug conjugates, which are immobilized on the test zone, compete for binding to specific antibody conjugates, which are mobilized as the applied test specimen migrates on the device. If the drug in the urine is present above threshold (cutoff) concentration, it will bind all the antibody conjugates leaving no antibody conjugates to bind with the immobilized drug conjugates to form a color line. Thus, the end point for a specimen containing drug at concentration at or above below threshold is absence of a color line; that for a negative specimen is the presence of a color line—a negative-indicating reaction. Most of the devices also have control lines to serve as internal quality control.

The accuracy of testing by these devices, however, is dependent on the experience and training of the operators (51,52).

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