Institute of Forensic Medicine, University of Düsseldorf, FRG

Transcription

1 COMPARISON BETWEEN THE RESULTS OF BLOOD AND BREATH ANALYSES OF DWI-DRIVERS Freudenstein, P., Huckenbeck, W., Schmidt, P., Bonte, W. Institute of Forensic Medicine, University of Düsseldorf, FRG SUMMARY In 1983 in the catch area of the Institute of Forensic Medicine, a new breath analyzer (Draeger 7310) was introduced as a screening system for persons arrested on suspicion of driving under the influence of alcohol. This paper reports on all cases from the years 19 to 19 in which a breach test was followed by a blood ethanol analysis. The adjusted BACs were compared to the breach alcohol values. Our data suggest that the fear of false positive results in breach analysis may produce something similar to an inflation of the legal limit. The problems for traffic safety are discussed. INTRODUCTION The question of blood or breach analysis has become important in German since the introduction in 1983 of a commercially valuable digital breach analyzer "Draeger 7310". In laboratory tests this breach analyze was able to produce results which differ only in a narrow range from blood analyses. At present here is a controversial discussion about the necessity of a correction factor depending on the breath temperature. As a consequence it seems, as if the breath test is going to displace blood-alcohol analysis in near future. There is some resistance to this trend coming from medico-legal experts, but they are financially partly involved. The same is also true for the companies which try to introduce the breach test as the only legal test for alcohol. As a consequence the arguments of both sides were evaluated with great reserve. But there is one argument, which should be kept in mind. The main question is, whether laboratory tests reflect the real roadside situation. There is some evidence that blood-breath comparisons in the laboratory yield different results from those at the roadside, many factors may influence the latter: For example there are no standardized conditions. There many be difficulties in calibration by non-specialists and there is a difference between breath sampling of volunteers and actual delinquents. This may be the reason why research groups, especially in Central Europe stated, that breach analyses taken at roadside to not correlate as well to blood analyses, as in the laboratory tests. This paper will confirm these observations, and it will demonstrate that the fear of false positive results in breath analyses seems produce something like an inflation of the legal limits. RESULTS In the blood sample records of 6,912 blood samples analyzed in the Institute of Forensic medicine at the University of Duesseldorf, Federal Republic of Germany from 19 to 19, the results of roadside breath tests were registered. When comparing the officially tested breath and blood results one must take into consideration that the blood sample for BAC analysis, is as a rule, taken some time later than the breath tests. This may be a problem, but we will try to 243

2 minimize it. In our first comparison of blood and breath values (Table 1) we recalculated the blood alcohol content assuming hourly decrease of.12 promil. That is a very low decrease. According to the legislature the four single blood values are not allowed to differ more than + 10 percent from the mean value. We decided therefore, that a breath value differing form the blood mean value within the range should be considered correct. During the years 19 to 19 only abut 28 to 35 percent of the breath measurements reflected the real blood concentration correctly. It is remarkable, that the percentage of breath results with too low values is increasing over the years. The correct results are in the range of about 30 to 35 percent and there is a small decrease over the course of the years. As a conclusion, it is our opinion, that breath analyses at the roadside do not sufficiently reflect the real blood values. One could think, that the difference between BAC and breath alcohol values was caused by our recalculation, but a significant influence of this procedure cannot be demonstrated. In more than 82 percent of the cases the recalculation did not exceed one hour (Table 2.) And this means, that the possible error is only small. Nevertheless there is another possibility to avoid any error caused by recalculation. One can compare the breath value with the blood vale directly. it becomes obvious, that omission of the recalculation results in a shift to the positive side. But, once more, only 32 to 37 percent of the breath values are within the tolerance limits, and logically, the percentage of breath values are higher than the actual back increases. The difference between blood and breath calculated on recent basis are influenced by the actual blood concentration. One could think, that the majority of low blood values might have influenced these figures. But this is not true as can be shown by analyzing false negative breath results, which are more than 30 recent lower than the respective BACs, in relationship to the difference ranges (Table 4). Over the year there is a trend towards a higher percentage of too low breath values. This trend is very significant in the range below.8 promil, but it is also significant int he other ranges. This means, that the breath analyzers must have been calibrated lower and lower over the years to avoid false positive results. So let us compare the data of the false positive breath estimations, that i to say more than 30 percent difference (Table 5). Within the ranges of less than 1.3 promil a respective tendency cannot be demonstrated. But on the contrary, and at the same time, there is a trend towards false positive breath results, as far as blood values above 1.3 promil are concerned. There is also rather good argument with this trend shown above for too low values. The problem of recalculation may be influenced by the actual pharmacokinetics status. Those, who stopped drinking jut before control, might possibly have a low breath value, but a high BAC, because the blood sample was taken later than the breath test. It is known, that in such cases of lasting absorption and increasing blood values, alcoholic impairment is much more serious than during the elimination phase. We also tried to elucidate this phenomenon. In Germany, in all cases of blood sampling the respective physician must carry out some performance tests with the offender because of DWI, and he must evaluate the results to register the degree of drunkenness. There can be three results. The offender may be less alcoholized then would be expected according to BAC. he may be suitably alcoholized, or he may be higher alcoholized than expected. In the latter case it is likely, that the blood sample of the respective 244

3 offender was taken during the absorption phase. This means, that the breath sample taken earlier int he absorption phase should display a lower value than that of the blood sample taken later. As a conclusion, one could think that our results have been influenced b this fact. But obviously this explanation is not correct either. Of those reasons underestimated by breath analyses in a range of more than 10 percent, those with a relatively low degree of drunkenness are over represented and the figures degrees with increasing degree of drunkenness (Table 6). Of course there is to eh same trend in cases where the breath results are more than 30 percent below the blood results. There is a small increase. But, jus a mention it, the figure of 25.5 percent of this category consists of only 16 cases compared only to this class of delinquents. And our total figure is 6,912 (Table 7). DISCUSSION To our opinion the harmful taking of a blood sample may be replaced by a breath test. But the officials must know, that false negative, as well as false positive results are a realistic risk. Our figures show, that our officials are aware of this fact, and tend to calibrate towards lower breath levels to avoid false positive results. The result is, that about 60 percent of the offenders were estimated too low when relying on the breath test. Looking at the figures of blood alcohol values just below.8 promil which is legal limit in Germany, the trend of 29.7 percent towards 8.3 percent over the years seems to indicae, that the fear of false positive findings enforces something similar to an inflation of the legal limit. Forensic experts in Germany tent to propose the.5 promil limit. But, the replacement of blood by breath tests will produce a contrary: The probability of being caught by breath tests with blood alcohol concentrations above 1.0 promil is very low. Locally, this limit may be reduced to.8 promil with a legal limit of.5 promil. but what is the sense? Reducing the legal limit to.5 promil when preferring breath test does not result in anything more than remaining at the present status. 245

4 (REL. FREQUENCY) 86 BREATH ALC. <BAC BREATH ALC. =BAC (±10 X) BREATH ALC. >BAC Table 1: Comparison o f b re a th and r e c a lc u la te d b lo o d a lc o h o l c o n c e n tra tio n n=6912 ABSOLUTE < 1 hour hours hours hours > 4 hours Table 2: Time d iffe r e n c e between b re a th t e s t and b lo o d sam pling (REL. FREQUENCY) CO CO K BREATH ALC. <BAC BREATH ALC. =BAC (±10 ) BREATH ALC. >BAC Table 3: Compari son o f b re a th and b lo o d a lc o h o l c o n c e n tra tio n w ith o u t r e c a lc u la t io n 246

5 BAC (G/L) 86 < > Table 4: B re a th a lc o h o l < BAC D iscre pancy o f more than 30 BAC (G/L) 86 < > Table 5: B reath a lc o h o l > BAC D iscre pancy o f more than

6 DRUNKENNESS n n BREATH < BAC * BREATH < BAC UNDERESTIMATED UNDERESTIMATED ADEQUATE OVERESTIMATED OVERESTIMATED Table 6: Degree o f drunkenness in people with b re a th a lc o h o l < BAC (d is c re p a n c y > 10 ) DRUNKENNESS n n BREATH < BAC BREATH < BAC UNDERESTIMATED UNDERESTIMATED ADEQUATE OVERESTIMATED OVERESTIMATED Table 7: Degree o f drunkenness in peo ple with b re a th a lc o h o l (d is c re p a n c y > 30 ) < BAC 248

7 FIGURE 1 ESTIMATED PROPORTION OF DRIVERS INVOLVED IN FATAL CRASHES WHO WERE DRINKING OR DRUNK FIGURE 2 ESTIMATED PROPORTION OF DRIVERS, BY AGE, INVOLVED IN FATAL CRASHES THAT HAD A BAC > OR = A G E -G R O U P S o ^ 45 ond OLDER 249