New Findings on the Normal Range of Gamma-Glutamyl-Transferase and their Importance for Driver Aptitude Testing

Transcription

1 New Findings on the Normal Range of Gamma-Glutamyl-Transferase and their Importance for Driver Aptitude Testing Manfred Weinand Bundesanstalt für Straßenwesen Brüderstr. 53 D-5060 Bergisch Gladbach 1. Introduction In the Federal Republic of Germany drivers whose driving licences have been withdrawn because they were caught driving under the influence of alcohol (DUI) and who have given cause to doubt their aptitude as a driver are required by the authorities to submit to a medical and psychological examination before a new licence may be granted. The interview regarding alcohol consumption is a key element of such an examination. Since the testing method is quite transparent (Undeutsch, 1982), the experts are often faced with the drivers' tendencies to belittle and conceal their alcohol consumption in order that the report be positive and the aim of obtaining a new licence be achieved. In particular alcohol endangered persons tend to play down or even totally deny their alcohol intake. By employing this uncritical strategy they try to deceive not only their social environment but often also themselves as to the real extent of their alcohol problem. Because of the tendencies of falsification and concealment, the experts generally cannot do without objective medical findings (Kriegeskorte, 1981; Haffner et al., 1989). In this context the determination of gamma-glutamyl-transferase (GGT) has proved to be a sensitive indicator as well as an economical source of information. There are a great number of studies to confirm the close relation between an increase in GGT activity and considerable alcohol consumption. Among others, Poser et al. (1978), Geiselbrecht et al. (1978), Müller-Alberti and Kessel (1988) have studied this issue. With respect to GGT activity in the serum of adults, a range up to 28 U/l for males and up to 18 U/l for females, measured at 25 C, is considered as the "normal range" in the Federal Republic of Germany so far. In Boehringer's booklet on the determination of GGT activity the reference for these values is merely mentioned as "Szasz, G., persönliche Mitteilung" (personal communication). Exact data on the composition of the standard population have not hitherto been found by the author of this paper. However, the normal ranges have presumably been obtained from an unselected (healthy) sample of the German population. The percentage of the German population practising complete abstinence from alcohol is relatively small, but there is a large number of people who drink alcohol to a lesser or greater degree and, based on recent estimates (Stephan 1990), in the old federal states there are about Alcohol, Drugs and Traffic Safety - T92 Ed. by Utzelmann / Berghaus / Kroj Verlag TÜV Rheinland GmbH, Köln

2 million drinkers requiring treatment. According to Kornhuber et al. (1989) the definition of the GGT range so far considered normal was based on a population which, as a whole, is under the toxic influence of daily doses of alcohol, so that instead of the health standard only the pathological average could be determined. Meanwhile new research results have become available on the normal range of GGT. These findings, their use in the examination of DUI offenders and their general impact on driver aptitude testing form the content of the following sections. 2. State of research Past research findings (Weißhaar et al., 1974, Poser et al., 1978) have already indicated that the upper limits of the normal range of GGT are too high. Recent epidemiological studies by Kornhuber et al. (1989, 1990) confirm these findings. Kornhuber's research team assumed that a real validation of GGT is only possible by means of external criteria. Blood pressure, pulse rate, deposits of fat and serum insulin are suitable external validation factors since they are known to change in people under the influence of alcohol. In a large sample of adult patients (n = 1379) with suspected neurological conditions, where the final diagnosis did not show any of the known correlations with raised blood pressure, obesity or changes in liver enzymes, and in a smaller group of patients (n = 223) without liver-related diseases, the investigations revealed that most of the pathological changes (increase in blood pressure, pulse rate, serum insulin and relative body weight in terms of the Broca Index) correlate precisely with the range of GGT values which have so far been considered as normal. Persons with GGT 9-12 U/l have a significantly higher blood pressure than persons with GGT up to 8 U/l. The relationship between blood pressure and GGT is the same for men and women; in both, the steepest increase is just in the low GGT range between 9 and 25 U/l (Kornhuber et al., 1989). Furthermore, Kornhuber et al. (1990) found that the sum of the three transferases, i.e. gamma-glutamyltransferase (GGT), aspartate aminotransferase (glutamic-oxalacetic-transaminase, GOT) and alanine aminotransferase (glutamic-pyruvic-transaminase, GPT), increases in proportion to the reported alcohol consumption (g/day). A sum of the transferases up to 20 U/l is an indication of abstinence, while a sum of the transferases above 60 U/l is an indication of consumption of about 50 g alcohol/day. An investigation by Kornhuber, which is still not completed, appears to confirm his previous research findings (personal communication). With respect to the examination of DUI offenders, the most important research finding of these recent investigations is that "including measuring inaccuracy the really normal range of GGT is up to 12 U/l" and "the really normal sum of GGT + GOT + GPT is only up to 36 U/l" (Kornhuber et al., 1990, p. 136). 148

3 3. The new normal ranges in driver aptitude testing: First experience and knowledge Since 1990 the research findings of Kornhuber et al. have been used in the examination of DUI offenders at the "Obergutachterstelle für das Land Nordrhein-Westfalen zur Beurteilung der Eignung von Kraftfahrzeugführem" (an appellate board of experts for the evaluation of driving aptitude in the State of North-Rhine Westphalia), headed by Prof. Undeutsch. First experience with the use of the new findings in examining drivers is therefore now available; it is described in the following in conjunction with the data evaluations undertaken thus far. 3.1 Results from case studies Psychological examination of DUI offenders rapidly revealed that the new findings, both for GGT and the sum of the transferases, are of great use in the exploration of alcohol consumption. With the new limit values, reported alcohol consumption can be more adequately checked, reported abstinence from alcohol can be more readily disproved and periods of abstinence can be better controlled than with the conventional limits. One of the many cases is described here in order to illustrate this point. An examination carried out in May 1990 on a driver with three alcohol-related traffic offences in the past (BACs of 1.64 %o, 2.24 %o and 1.82 %o) revealed an irrefutable abstinence from alcohol for a period of about nine months. The laboratory tests conducted in April 1990 yielded results (GGT and sum of the transferases) in the new normal ranges. Based on these and other findings, a low probability of the driver's relapse was predicted. However, based on doubts about the durability of his abstinence once he had regained his driving licence, a re-examination and the regular production of relevant laboratory test results were recommended in the expert report. Under these conditions the subject was granted a new driving licence. A re-examination with the determined laboratory results took place in March For reasons of space, only the values illustrating the changes are listed in the table below: Date GOT GPT GGT Sum of transferases

4 The results show that the driver's assertion of continued abstinence from alcohol is not borne out by the values listed. After regaining his licence, his GGT rose from 11 U/l to 18 U/l and 19 U/l, and the sum of the three transferases increased from 26 U/l to 64 U/l and 92 U/l. But in view of the impending reexamination the values decreased to finally lie again within the new normal ranges. Considering these findings, the driver's assertion of abstinence was very intensely questioned with the result that he gave up the strategy of concealing his drinking and admitted that after regaining his licence he had been drinking 2 or of beer from time to time. The last such occasion was in January 1992, when he consumed of beer. Since then, however, he has only been drinking occasionally and never more than a bottle of beer (0.5 1). The changes in his alcohol consumption are thus reflected in the corresponding development of the test values. 3.2 Targeted evaluation of expert reports After Kornhuber's research results had been introduced, it was noticed in the course of time that DUI offenders examined at the appellate board of experts increasingly presented lower GGT values than the drivers in previous years. Based on these findings, the expert reports were evaluated to clear up the question of whether the reduction in GGT is statistically significant or not. In addition, the data were analysed specifically for correlations between GGT values and alcohol consumption as well as between sums of transferases and alcohol consumption Material and methods For a before-and-after comparison a random selection of 110 examined cases for each of the years 1988/89 and 1991/92 was made based on material filed at the appellate board of experts. The sample thus comprised a total of 220 DUI offenders; 208 males (94.5 %) and 12 females (5.5 %) with an average age of 42 years. The subjects have, on average, two offences with a mean BAC of 1.95 %o. In addition to the BAC value established at the time of their last offence, the laboratory results on GGT, GOT, GPT and MCV (mean corpuscular erythrocyte volume) prior to the examination and, as a rough indication of their alcohol consumption, the maximum amount of alcohol consumed (in g) during the last six months as reported by the subjects in the exploration were included in the data analysis. Alcoholics, drug users and persons with liver-related diseases, or those taking medicaments affecting the liver enzymes, were excluded from the analysis. The data were evaluated by means of the SPSS/PC + statistics software, version 4.0. The nonparametric U-test (Mann/Whitney) was used to compare the samples; the correlative relations were determined by means of Spearman's coefficient of rank correlation. The significance level was set at 5 %. 150

5 3.2.2 Results The statistical evaluation revealed that the persons examined had altogether lower GGT values in 1991/92 (median: 15.0 U/l) than in 1988/89 (median: 21.0 U/l). The same applies to the sum of the transferases (38.0 U/l vs U/l). The differences proved to be statistically significant (p < 0.01). Both samples also differ significantly with respect to the number of DUI offences, maximum alcohol consumption and GPT value (p < 0.05); in 1988/89 all values were, on average, higher. The other variables (age, BAC values, GOT, MCV) did not change significantly in the period of investigation. A comparison of those persons in the two samples who had reported abstinence from alcohol in the interview (1988/89: n = 27; 1991/92: n= 46), revealed that GGT values and the sums of the transferases in 1988/89 (medians: 19.0 U/l and 45.0 U/l) had been overall higher than in 1991/92 (12.0 U/l and 32.5 U/l). The differences between these samples are also statistically significant (p < 0.001). Whereas in 1988/89 only 14.8 % of the reportedly abstinent persons produced GGT values up to 12 U/l, the percentage during the period in question after the new normal range had been introduced (1991/92) rose to 56.5 %. The same applies to the GPT values which in the reportedly abstinent persons examined in 1991/92 were lower on average than in 1988/89 (p < 0.05). A statistically significant difference in respect of the number of alcohol offences in the two subgroups asserting abstinence was no longer found (p = 0.08). The groups of persons who admitted to alcohol consumption do not differ significantly during the two observation periods with regard to GGT and the sum of the three transferases. The analysis of the data from the appellate board of experts further demonstrates that the GGT values of the subjects in 1991 and 1992 and the sums of the transferases correlate significantly with the reported alcohol consumption (R = 0.45, p < 0.01 and R = 0.37, p < 0.01), with the relationship between GGT and alcohol consumption being somewhat stronger. The data collected before the introduction of the new findings did not yield any such significant correlations. 4. Discussion The experience gained at the appellate board of experts (North-Rhine Westphalia) with the use of the new findings on the normal ranges and the results of the evaluation reveal that the research findings of Kornhuber et al. are a step in the right direction. The new GGT limit and the new normal range of the sum of the three transferases have proved to be fully successful in the examination practice. They facilitate the work of experts in exploring the alcohol consumption and in checking abstinence statements and provide a better contribution to the reliability of the prediction than has been possible by means of the limits applicable hitherto. In view of the known uncertainties connected with the exploration of alcohol consumption within the scope of driver aptitude testing and of the fairly rough operationalization of alcohol consumption in our evaluations, the correlations 151

6 between alcohol consumption and GGT and between alcohol consumption and the sum of the three transferases are thoroughly remarkable. The relations mentioned are also only found in cases examined after "Komhuber's values" had been introduced. This result, in connection with the decrease in GGT values measured in persons reporting abstinence in 1991/92, can be considered as an indirect confirmation of the correctness of the narrower normal ranges. The decrease in GGT values in people reportedly not drinking might, at least in part, have been effected by "Komhuber's standards", apart from other possible factors of influence, such as e.g. changes in drinking attitudes and behaviour; further research would be necessary to clarify this. Some of those who had to submit to a psychological examination at the appellate board of experts lately (1991/92) had presumably already taken note of the narrower normal ranges and had consequently restricted or given up their alcohol consumption prior to the examination. A tendency toward "norm-conforming results" was also found in a comparison with first-time alcohol offenders with high BACs examined by a different authority in 1979 and 1981 (Sliwka, 1983). In these examinations, the GGT values measured in 1979 were often higher than those recorded in This correlates well with the information provided by drivers in the course of examinations, namely that in view of the impending tests they had followed the advice given them by others, i.e. to abstain from alcohol or drastically cut down on their drinking for some time. It should not be overlooked in this context that GGT, even though it does react with high sensitivity to increased alcohol consumption, also proves to be of rather limited diagnostic specificity (Große Aldenhövel, 1984). Raised GGT values must therefore be interpreted with care. Since exclusion diagnoses in the presence of increased GGT values are often difficult to make, interviews on alcohol consumption conducted by competent psychologists are of crucial importance in examining DUI offenders. This key element of driver aptitude testing - as our experience shows - can be effectively supported by the new normal ranges and thus can contribute considerably to improving the accuracy of experts' prediction. 5. References Geiselbrecht, W., Krüger, D. and Winkel, M. (1978): Die Gamma-Glutamyl- Transferase als Diagnostikern im forensischen Bereich am Beispiel der Eignungsuntersuchungen alkoholauffälliger Kraftfahrer. Blutalkohol 15, Große Aldenhövel, H. (1984): Erhöhte Serumaktivitäten von Gamma-GT und Transaminasen im Rahmen verkehrsmedizinischer Eignungsuntersuchungen alkoholauffälliger Kraftfahrer: einige differentialdiagnostische Gesichtspunkte. Blutalkohol 21, Haffner, H.-T., Becker, I.-S. and Mann, K. (1989): Zur Sensitivität klinischchemischer Marker des Alkoholismus nach kurzfristiger anlaßbezogener Alkoholkarenz. Blutalkohol 26, Komhuber, H.H. et al. (1990): Die Hauptursache von Diabetes (Typ II): der "normale" Alkoholkonsum. Versicherungsmedizin 42,

7 Komhuber, J. et al. (1989): GGT-Normbereich bisher falsch definiert: Zur Diagnostik von Bluthochdruck, Adipositas und Diabetes infolge "normalen" Alkoholkonsums. Versicherungsmedizin 41, Kriegeskorte, E. (1981): Der Stellenwert der Gamma-Glutamyl-Transferase in der Medizinisch-Psychologischen Kraftfahreignungsuntersuchung. Zeitschrift für Verkehrssicherheit 27, Müller-Alberti, A. and Kessel, R. (1988): Korrelation zwischen Alkoholkonsum und Laborbefunden bei gesunden männlichen Arbeitern. Arbeitsmedizin, Sozialmedizin, Präventivmedizin 23, Poser, W. et al. (1978): Erhöhung der GGT-Aktivität im Serum bei Alkoholismus und chronischem Mißbrauch von Schlafmitteln. Nervenarzt 49, Sliwka, N. (1983): Fahreignungsuntersuchungen nach erstmaliger Verurteilung wegen Trunkenheit am Steuer bei hoher Blutalkoholkonzentration. Zeitschrift für Verkehrssicherheit 29, Stephan, E. (1990): Leistungsmindemde Suchtstoffe im Straßenverkehr. In: Deutsche Hauptstelle gegen die Suchtgefahren (ed.): Jahrbuch Sucht 1991, Undeutsch, U. (1982): Bedeutung und Aufgaben der Exploration bei der Prognose der Rückfallwahrscheinlichkeit in ein Alkoholdelikt. In: Winkler, W. (ed.): Verkehrspsychologische Beiträge I, Schriftenreihe "Faktor Mensch im Verkehr" 32, Weißhaar, D. et al. (1974): Normbereiche von Gamma-Glutamyltranspeptidase und - bei Messung mit substratoptimierten Testansätzen - von SGPT und SGOT. Med. Welt 25,