Info

Blood,

urine, oral fluid

3/1

Prison/lab

Laboratory personnel

representatives from some manufacturers as assistants. The oral-fluid tests (Cozart Rapiscan [Cozart Bioscience Ltd.] and Drugwipe® [Securetec Detektions-Systeme AG]) were performed at the police station.

• Spain: on-site tests were performed by agents of the traffic police. Reading and interpretation of the results were done together by members of the Institute of Legal Medicine present during the patrol and by traffic police officers trained in the use of the devices. With one exception, the tests were performed at the roadside.

• United Kingdom: the subjects were prisoners. The on-site tests were performed by at least two members of the research team, either in the prison or in the laboratory.

The data from the evaluations in the eight countries were displayed in Microsoft Excel format. For the evaluation of opiates, specimens containing morphine, 6-acetylmorphine, or codeine were considered positives. It should be noted that other substances may cross-react and give positive results with on-site tests—for example, dihydrocodeine or pholcodine. For determination of the optimal cut-off levels in oral fluid, receiver operating characteristic (ROC) curves (7)) were used.

Several comparisons were made between the different methods (on-site tests or reference methods) and the different matrices (blood, urine, oral fluid, or sweat). For each drug class, the following comparisons were made:

• A comparison between the reference method for blood and for the other biological fluids was made in order to assess whether findings in each matrix correspond well to those in blood. There is a general consensus that blood is the standard reference, as impairment (or recent exposure to drugs) corresponds best to the presence of drugs in blood;

• A comparison of on-site device results with those obtained from the reference methods for the same matrix;

• The validity of the roadside test for predicting blood positives by comparison with the results of blood samples assessed with a reference method.

For evaluation of the urine, oral-fluid, or sweat test devices, the accuracy, sensitivity, and specificity values have been calculated on the basis of the following definitions, where TP = true-positives, TN = true-negatives, FP = false-positives, and FN = false-negatives:

• Accuracy = percent of all samples correctly identified by the tests = (TP + TN)/ (all results)

• Sensitivity = true-positives expressed as percent of all positives = TP/(TP + FN)

• Specificity = true-negatives expressed as percent of all negatives = TN/(TN + FP)

The following analytical criteria for an acceptable test were used: accuracy >95%, sensitivity >90%, specificity >90%, when compared with a reference method. Statistical analysis of the data was performed using Microsoft Excel, Medcalc (MedCalc Software), and SPSS (SPSS, Inc.).

3.4.2. Results

The study was performed on 2968 subjects. Ninety-two percent were males. Before evaluating the performance of on-site test devices, positive and negative results of a given drug class in oral-fluid, sweat, and urine samples assessed by a reference method (e.g., GC-MS) were compared with the results of blood samples assessed by the same reference method. This process allowed for the computation of the sensitivity, specificity, and accuracy of using a given reference method (e.g., GC-MS) in different fluids. In general, one can conclude that the accuracy rate of such comparisons using GC-MS ranges between 78 (cannabinoids in sweat) and 99% (cocaine in oral fluid) (Table 3). The exception is the benzodiazepine group, where the low sensitivity of the analytical methods applied in the laboratory appears to be the cause for the overall low and insufficient accuracy rate of oral fluid (29%) as a specimen for roadside screening. It is clear that there will never be a 100% correlation among the different body fluids. The results are influenced by the timing of sampling relative to the last drug intake. If a drug was taken very recently, it is possible that it can be found only in blood (and oral fluid), but not yet in urine. If a drug was taken a longer time ago, it is possible that it is no longer detectable in blood, but only in urine (and possibly in sweat).

In the next set of experiments, drug results from oral-fluid, sweat, and urine samples as assessed by various on-site testing devices were compared with those of the same fluid assessed by the reference method (i.e., GC-MS) or those of blood samples assessed by the same reference method. These results are given in Tables 4-6. The following sections provide a summary of the findings.

For amphetamines, all body fluids were appropriate for testing of this drug when GC-MS was the reference method. Both urine and oral fluid have good accuracy and predictive values (Table 3). Eighteen different on-site tests for amphetamine or methamphetamine were evaluated. If the results of amphetamines and methamphetamine were considered jointly (i.e., if one considers the test to be positive if either the amphetamine or the methamphetamine test is positive), test devices such as Rapid Drug Screen® (RDS; American Bio Medica), Dipro, and Syva® RapidTest™ (SRT; Dade Behring) satisfied the analytical criteria (accuracy >95%, sensitivity >90%, specificity >90%) (Table 4). Tests for oral fluid had much lower accuracy (80% or less in all cases; Table 5). The optimal cut-off for amphetamines in oral fluid was in the range of 70-90 ng/mL. For sweat, the low number of samples (nearly all positive) did not permit definite conclusions (Table 6), but use of sweat seemed promising.

Urine seemed to be a better fluid for detecting benzodiazepines at the roadside with the reference methods used (Table 3). Of the on-site urine test devices, Triage (Biosite Diagnostics) and RDS were the only two that met the

Table 3

Comparison of the Accuracy, Sensitivity, and Specificity of the Qualitative Results by Gas Chromatography (GC)-Mass Spectrometry (MS) in Urine, Oral Fluid, and Sweat vs GC-MS in Blood ("Gold Standard") for the Different Drugs

Table 3

Comparison of the Accuracy, Sensitivity, and Specificity of the Qualitative Results by Gas Chromatography (GC)-Mass Spectrometry (MS) in Urine, Oral Fluid, and Sweat vs GC-MS in Blood ("Gold Standard") for the Different Drugs

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