conclusive, it appears that the originator of this scheme was Applicant 1 who spiked her urine sample with a pharmaceutical preparation such as Tylenol | with ...
Journal of Analytical Toxicology, Vol. 14, May/June 1990
Letters to the Editor conclusive, it appears that the originator of this scheme was Applicant 1 who spiked her urine sample with a pharmaceutical preparation such as Tylenol| with codeine or equivalent. Specimen adulteration is a very real problem for drug testing laboratories, particularly when sample collection is out of their direct control. As employee drug testing becomes more prevalent and as drug users become increasingly desperate, creative sample adulteration, and substitution techniques will no doubt escalate. Three important conclusions are supported by this report. First, the incidents of intentional adulteration of urine samples reported here demonstrate another reason for witnessed urine sample collection procedures. Second, the use of quantitative confirmation techniques, particularly GC/MS, generally allow discrimination between true positive urines and false positives associated with the in vitro addition of pharmaceutical preparations to urine. Third, effective and timely communication between employer and laboratory is crucial to the understanding and appropriate resolution of these circumstances. While the vast majority of sample adulteration attempts will be aimed at producing false negative results, the cases described in this letter indicate that intentional adulteration designed to produce false positive results can also occur. C.A. Johnson and EL. Cary Toxicology and Drug Monitoring Laboratory University of Missouri Hospital & Clinics 301 Business Loop 70 West, Suite 208 Columbia, Missouri 65203 References
1. National Institute of Drug Abuse. Urinalysis Collection Handbook for Federal Drug Testing Programs, September 1988. 2. J. Manno. Specimen collection and handling. In Urine Testing for Drugs of Abuse. NIDA Research Monograph #73, pp. 24-29 (1986). 3. S. Mikkelsen and K.O. Ash. Adulterants causing false negatives in illicit drug testing. C/in. Chem. 34:2333-36 (1988). 4. T. Vu Duc. EMIT tests for drugs of abuse: interference by liquid soap preparations. C/in. Chem. 31:658-59 (1985). 5. H.J. Kim and E. Cerceo. Interference by NaCI with the EMIT method of analysis for drugs of abuse. C/in. Chem. 22:1935-36 (1976). 6. S.D. Pearson, K.O. Ash, and F.M. Urry. Mechanism of false negative urine cannabinoid screens by Visine eyedrops. C/in. Chem, 3 5 : 6 3 6 - 3 8 (1989). 7. A. Warner. Interference of common household chemicals in immunoassay methods for drugs of abuse. C/in. Chem. 35:648-51 (1989). 8. J.T. Cody and R.H. Schwarzhoff. Impact of adulterants on RIA analysis of urine for drugs of abuse. J. Anal Toxico/. 13:277-84 (1989). 9. P.A. Lambert. Detection of sample contamination of urine submitted for drugs of abuse testing in a high volume setting using the Olympus 5000 Analyzer. C/in. Chem. 33:977 (1987).
Using a Weighted Mean to Compute the Values of Simulator Solution Standards To the Editor:
The accuracy of breath alcohol measurements is determined by the measurement of known standards and requiring that the systematic error be less than some appropriate level (i.e., + / - 5 % ) . This is typical of all analytical measurements. The measurement of known and traceable standards is the basis for determining accuracy and thereby confidence in all analytical results. The accuracy of breath alcohol instruments is typically determined through the use of simulator devices containing an aqueous ethanol solution (1). If the simulator is to be the known reference standard then it is fundamentally important that the concentration of ethanol in the headspace vapor be known. This is determined by employing the mathematical model described by Henry's Law. This model has been empirically derived and verified as it relates to simulator devices (2). Fundamental to knowing the headspace concentration of ethanol is knowing the aqueous solution concentration of ethanol. Simulator solutions are prepared by following an appropriate protocol and then measuring the concentration of ethanol by a variety of methods. The results of these quantitative measurements are the basis for 196
Journal of Analytical Toxicology, Vol. 14, May/June 1990
Letters to the assigning a reference or known value to the simulator standard. The breath test instrument is then evaluated for accuracy against this " k n o w n " reference value. A commonly used method for determining the aqueous ethanol concentration is gas chromatography. It would seem a simple matter to perform several measurements on the batch of solution, compute the arithmetic mean, and call this the reference standard or target value. Depending on the measurement protocol, it may not be that simple. When the solution measurements are made by different individuals and on different days, the simple arithmetic mean may not be the best estimate of the true solution value. A weighted mean may be a more appropriate estimate of the true concentration. The results o f simulator ethanol concentrations determined by gas chromatography were recently evaluated. The protocol had six different forensic toxicologists perform five measurements each on a particular batch of aqueous ethanol solution. The results were reported to three decimal places. Frequently, the individuals performed their set of measurements on different days. The reference value of the solution was then computed as the arithmetic mean of all 30 measurements and reported also to three decimal places. The results o f these 30 measurements were used to compute the weighted mean and compare this to the simple arithmetic mean. In this case the arithmetic mean was computed to four decimal places, which is more appropriate than three since the data values themselves have three (3). The weighted mean is computed as follows (4,5): n
GW,x, --
i=1
X w = - - ~i=1
w,
where Wi
--
t/ S2
Wi is the weight to be applied to each mean and s: is the sample variance. The individual variances were then compared by the Fmax test for independent variances (6). The Finsx value is the largest sample variance divided by the smallest sample variance and is evaluated from the F distribution for 4.4 degrees of freedom with the present data. The results of the comparisons are seen in Table I.
Table I. Statistical Summary of Simulator Solution Values Batch 1 2 3 4 5 6 7 8 9 10
Arithmetic mean 0.1232 0.1235 0.1238 0.1231 0.1240 0.1234 0.1247 0.1240 0.1261 0.1249
Weighted mean 0.1223 0.1210 0.1234 0.1228 0.1248 0.1233 0.1249 0.1252 0.1268 0.1249
Arithmetic BrAC 0.1018 0.1021 0.1023 0.1018 0.1025 0.1020 0.1031 0.1025 0.1042 0.1033
Weighted BrAc 0.1011 0.1000 0.1020 0.1015 0.1032 0.1019 0.1032 0.1035 0.1048 0.1032
~
F* -.73 -2.07 -.35 -.30 .67 .11 .16 .95 .57 -.05
5.7 21.7 6.5 5.7 9.0 13.4 10.6 15.0 14.3 1.8
p< 0.05 x x x x x • x
9 Fmax test for equal variances, F05,4,4 = 6.39, F.01,4,4 = 15.98.
The results in Table 1 show that the differences in computed vapor alcohol concentrations varied from 0.05 to 2.07% when using the weighted mean as opposed to the arithmetic mean. The Fmax test was also significant (p < 0.05) in seven of the ten cases. Gas chromatography results that do not employ automatic injection can be subject to operator variability. Measurements made on different days can also introduce variability. When there is significant variability in an analytical method and the known concentration is the objective, then a weighted mean computation is probably more appropriate. The weighted mean computation attaches more weight to those groups of measurements that are more precise whereas the arithmetic mean attaches equal weight to all measurements. The significance of these results is seen when attempting to establish the limits of accuracy on a breath alcohol instrument. If the systematic error must not exceed _+5~ then an error of 2.07~ (as determined by weighted versus arithmetic mean) can make a significant difference. It would seem that a weighted mean provides a better estimate of the true simulator solution value and should be employed for those cases in which significant inter-operator or
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Journal of Analytical Toxicology, Vol. 14, May/June 1990
I Letters to the Editor interday variability exists. At the very least, the weighted mean should be compared to the arithmetic mean to determine if significant differences exist. This is particularly true when the Fmax value exceeds 5.39 (4.4 d.f.). The Fmax test, therefore, provides a useful index as to when further computation of the weighted mean may be necessary. R.G. Gullberg Breath Test Section "Washington State Patrol 6431 Corson Avenue South Seattle, Washington 98108 References 1. K.M. Dubowski. Breath-alcohol simulators: scientific basis and actual performance. J. Anal Toxicol. 3:177-82 (1979). 2. A.W. Jones. Determination of liquid/air partition coefficients for dilute solutions of ethanol in water, whole blood, and plasma. J. Anal ToxicoL 7:193-97 (1983). 3. S.L. Meyer. Data Analysis for Scientists and Engineers, John Wiley and Sons, New York, 1975, p. 26. 4. J. Mandel. The Statistical Analysis of Experimental Data, Dover Publications, New York, 1964, pp. 65-68. 5. J.R. Taylor. An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements, University Science Books, Mill Valley, California, 1982, pp. 148-51. 6. J.E. Freund. Modern Elementary Statistics, 4th ed., Prentice-Hall, Englewood Cliffs, New Jersey, 1973, pp. 293-97.
Status of Alcohol Absorption Among Drinking Drivers To the Editor:
The status of alcohol absorption in drinking drivers, that is, whether the blood-concentration-time curve is rising, on a plateau, or declining, has important medicolegal implications. First, the "rising blood-alcohol defense" is a well-proven litigation in drunk driving trials (1,2). This implies that the blood-alcohol concentration (BAC) was below the legal limit at the time of offence but above the limit when blood was obtained for forensic analysis. Second, a number of drunk driving statutes refer to the BAC existing at the time of offense or within 1-2 h thereafter, and not at the time blood specimens are obtained for analysis (3). This raises the issue of retrograde extrapolation and there are well-known problems and pitfalls associated with this practice (4-6). Third, during rapid absorption of ethanol from the gut, the concentration in venous blood might lag behind the concentration in arterial or capillary blood (7). If a pronounced arterio-venous BAC difference exists, the result of a breath test might overestimate the venous BAC (8,9). Quantitative evidential breath-alcohol analyzers, such as the Breathalyzer 900, are calibrated to estimate the coexisting BAC during the postabsorptive state. To my knowledge, there aren't any published studies that demonstrate the position of the blood-alcohol curve in suspected drinking drivers. Bolus dose experiments involving rapid consumption (5-30 min) of neat spirits (0.5i.0 g/kg ethanol) on an empty stomach are unlike the drinking practices of most DUI offenders (10,11). The BAC among drinking drivers ranges from below the legal limit to 0.45 g%0 w/v. The mode is between 0.15-0.17 g~ w/v in most countries and this high concentration probably reflects consumption of alcohol over several hours. According to many bolus dose (0.34-1.02 g/kg) experiments undertaken by our group during the past 15 years, 77% of subjects (n = 152) reach peak BAC in less than 45 min after the end of drinking and 97% in less than 75 min. After a dose of 0.80 g/kg in the form of a 20% v/v orange juice cocktail, consumed within 30 min, peak BAC occurred within 60 min after drinking in 92% of trials (n = 65). Shajani and Dinn (12) reported that the average time to peak BAC after the end of drinking was 35 min (range 17-68 min) when the alcohol was consumed as mixed drinks in moderate doses and over longer drinking times. Gullberg (13) tested 39 subjects who drank alcoholic beverages of their choice with and without food. He found that
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