Concerns About Accuracy of Analysis

Further complicating POCT is the shift in analysis from the laboratory to the point of collection. Decentralizing the analytical process of DOA testing places the burden of responsibility for analytical interpretation on the collector and potentially unskilled personnel. Visually read endpoints of test results, although quite simple in most pregnancy tests, is dramatically more complicated in DOA testing. Most DOA tests contain multiple analyses, testing for cannabinoid (tetrahydrocannabinol; THC), cocaine, amphetamine, morphine, and phencyclidine (PCP) on one or more lateral-flow strips. Included on each lateral-flow strip is a control, ensuring that the sample has migrated across the test area. A five-drug test will have one target zone for each drug analyte and one target control zone for each strip. Hence, a two-strip, five-drug panel will have a total of seven target zones. Most competitive binding assays produce a color indicator in the absence of the analyte. However, some tests produce a color reaction in the presence of the analyte. This can potentially confuse the collector into misinterpreting the test result, when using different products for different clients. Furthermore, the intensity of the color change varies with each drug-test target, often resulting in a mottled, nonuniform array of visual test lines. Several manufacturers indicate on the package insert that any presence of color change, no matter how faint it may appear, should be interpreted as a negative result. There is considerable subjectivity to the test-result interpretation, leading to potential false-negative and false-positive errors. Timing of the test is critical, and the interpreter must read the test result during the time indicated on the package insert, usually between 3 and 8 min. Improperly timed readings could potentially result in false-negative or false-positive results. Visual acuity, color vision, and lighting conditions may also play a role in the interpreter's accuracy in reading visually interpreted endpoints. Subjective interpretation, or translation of the analytical result from the test strip to the test result report, is of major concern in point-of-collection testing.

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