University of Tübingen, Department of Psychiatry, Addiction Research Centre, Osianderstrasse 24, 72076 Tübingen, Germany
Received 18 September 1998; in revised form 25 January 1999; accepted 16 March 1999
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ABSTRACT |
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INTRODUCTION |
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Although self-report is in general a valid and important diagnostic instrument (Maisto and O'Farrell, 1985; Babor et al., 1989
; Rosman et al., 1992
; Mundle et al., 1996
), more objective and effective screening instruments, such as biological markers, are needed. Traditional markers are the membrane-bound liver enzyme
-glutamyltransferase (GGT) and the mean corpuscular volume (MCV), an index of red blood cell size (Conigrave et al., 1995
). The difficulty of diagnostic accuracy has been a limiting factor, although these markers are widely available. The most effective marker has been GGT with a sensitivity of about 4060% and a specificity of about 80% (Mihas and Tavassoli, 1992
). A new marker for high alcohol consumption and alcoholism is carbohydrate-deficient transferrin (CDT). Early studies on CDT were promising and suggested high sensitivity and high specificity (Stibler, 1991
). Studies comparing the diagnostic value of CDT with other biological markers usually suggested the superiority of CDT, particularly because of its specificity (Litten et al., 1995
; Sillanaukee, 1996
). Recent studies comparing the sensitivity of GGT and CDT, however, have shown a similar or even higher sensitivity for GGT in detecting heavy alcohol consumption and alcoholism (Helander and Tabakoff, 1997
; Huseby et al., 1997
; Yeastedt et al., 1998
). Most studies have suggested that GGT and CDT appear to be independent and may therefore compliment each other. Their combined use is reported to increase diagnostic sensitivity with little loss of specificity (Litten et al., 1995
; Sillanaukee, 1996
; Yeastedt et al., 1998
).
Factors influencing biological markers are duration of abstinence, age and alcohol consumption. The duration of abstinence before blood testing can cause differences in study results, especially for CDT, which has a relatively short half-life of 15 days (Behrens et al., 1988; Stibler et al., 1988
). Nevertheless, the time since the last drink is included in only a few studies. General conclusions from study results are therefore limited in scope (Litten et al., 1995
). The effects of age have also been reported in only a few studies. These indicate that GGT and MCV increase with age (Whitfield et al., 1978
; Sillanaukee et al., 1998
). Yersin et al. (1995) observed an increase in sensitivity in older patients from 56 to 74% for GGT and an increase from 17 to 39% for MCV. Daeppen et al. (1998) found a 64% average increase in GGT over a 15-year period in alcohol-drinking, but non-alcoholic, males, independent of alcohol consumption. The effect of age on CDT is inconsistent. Nystrom et al. (1992) recommended serum CDT for detecting early heavy drinking in young students, although the sensitivity was relatively low. Yersin et al. (1995) and Huseby et al. (1997) found that CDT values decreased with age; test results were highest in younger patients. Agelink et al. (1998) found that CDT was more sensitive in patients over 40 years of age than in younger patients. Conigrave et al. (1995) concluded that the sensitivity of all three markers is lower for hazardous consumption than for alcohol dependence: 2060% vs 6090% for CDT and GGT, and 2030% vs 4050% for MCV.
The aims of this study were to compare the sensitivities of CDT, GGT and MCV in a large clinical sample of male alcohol-dependent patients entering a 6-week in-patient treatment programme (Mann and Batra, 1993) and to analyse the factors influencing the test results of all three markers.
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PATIENTS AND METHODS |
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A baseline evaluation, carried out at the beginning of the in-patient programme, included a structured interview on alcohol history and social status (Mann, 1992), whose validity and reliability has been shown to be good (Mann et al., 1997
). In addition, a physical examination and laboratory and psychological tests were performed. The diagnosis of alcoholism was established according to DSM III-R (American Psychiatric Association, 1987
) and ICD-10 (World Health Organization, 1992
). Exclusion criteria were drug dependence, severe psychiatric co-morbidity (i.e. schizophrenic or depressive episode) or significant medical illness (i.e. liver cirrhosis, tuberculosis or tumour). Patients using medication that might affect liver enzymes were also excluded from the study.
Biochemical analysis
Blood tests were performed at the beginning of the in-patient programme within 24 h of admission. They were performed at the clinical laboratory at the Medical Department of the University of Tübingen. For measurement of serum GGT and MCV the commercial kit reagents from Boehringer Mannheim (Mannheim, Germany) and Bayer Technikon H1 (Germany) were used according to the International Federation of Clinical Chemistry's recommended methods. GGT levels above normal were defined as GGT > 28 U/l at a measurement temperature of 25°C. The upper limit for MCV was 96 fl. Serum CDT was analysed using a commercial kit from Axis Biochemicals AS, which gives the result as a percentage of the amount of total transferrin. This kit uses micro-column ion-exchange separation of the transferrin isoforms and then quantification of the CDT isoforms by radioimmunoassay (Lyngbye et al., 1997). Normal CDT levels were defined as
2.0%.
Statistical analysis
Differences in sensitivities between CDT, GGT and MCV were compared using the McNemar 2-test. To analyse the effect of the duration of abstinence before the blood test, patients were divided in two groups (
4 days and >4 days). Differences between these two groups were calculated by Fisher's exact test.
To assess potential group differences of mean levels of CDT, GGT and MCV due to age and alcohol consumption, patients were divided into three subgroups (alcohol consumption: <60 g/day; 60200 g/day; >200 g/day; age: <35; 3550 and >50 years).
Factorial analyses of variance were performed to investigate the influence of alcohol consumption and age for each marker. To control for days of abstinence, these were entered as a second factor in the analyses of variance. This was necessary, because days of abstinence did not show a normal distribution and therefore could not be entered as a covariate. Age was entered as a covariate in the analyses of variance of alcohol consumption, and alcohol consumption was entered as a covariate in the analyses of age. t-Tests for the adjusted means were calculated to analyse differences between the subgroups according to age and mean alcohol consumption.
To assess the correlations between markers, Spearman rank correlations were calculated with days of abstinence, age and alcohol consumption partialled out.
Prior to these analyses, CDT and GGT underwent logarithmic transformation to normalize distributions and to make variance more homogeneous. The Statistical Analysis System (SAS Institute, 1989) was used for calculations.
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RESULTS |
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Age
The laboratory marker data as a function of age of patients are shown in Table 3 for both the
and >4 days of abstinence subgroups. In the two factorial analyses of variance, age showed a significant effect for MCV [F(2,173) = 4.04, P < 0.05], but not for GGT [F(2,172) = 0.10, P = 0.901] or CDT [F(2,172) = 0.66, P = 0.519]. Post-hoc analysis of adjusted means for MCV revealed that the younger group significantly differed from the middle group [t(176) = 2.295, P < 0.05] and from the older group [t(176) = 2.605, P < 0.05].
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Correlations
Significant Spearman rank correlations among the three biological markers were found for MCV and CDT (r = 0.15, P < 0.05%) and for MCV and GGT (r = 0.29, P < 0.001) (Table 4). There was no significant correlation between CDT and GGT (r = 0.11).
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DISCUSSION |
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The combination of markers enhanced sensitivity for alcoholism. A sensitivity of over 90% could be achieved by the combination of CDT and GGT. The combination of all three markers provided little further information. The increase in sensitivity using CDT and GGT conjointly confirms earlier studies, and is mainly explained by the fact that these markers increase independently and are not correlated (Litten et al., 1995; Huseby et al., 1997
; Yeastedt et al., 1998
). Also, in our study, there was no significant correlation between CDT and GGT. The combination of GGT and MCV was not as effective, because these markers correlated significantly.
MCV seems to be a marker of second choice for alcohol-dependent men. As CDT is not yet widely available and remains expensive, MCV is still, despite its low sensitivity, a useful tool for screening, particularly when used conjointly with GGT (Monteiro and Masur, 1985; Levine, 1990
; Seppä et al., 1996
; Sillanaukee et al., 1998
).
The strongest influence on the test results of CDT and GGT was duration of abstinence before blood testing. In patients with only a few days of abstinence CDT and GGT showed significantly higher sensitivities. This effect is probably caused by the relatively short half-life of CDT of 15 days (Behrens et al., 1988; Stibler et al., 1988
) and of GGT of about 4 weeks (Orrego et al., 1985
). Therefore, duration of abstinence before blood testing should be considered in research studies and in clinical practice, otherwise results of CDT and GGT could be difficult to interpret (Litten et al., 1995
; Agelink et al., 1998
). Since MCV has a relatively longer half-life of 2 to 3 months (Renwick and Asker, 1982
), it was not as susceptible to the influence of this factor. In clinical practice, MCV should also be measured if there is a longer period of abstinence suspected (Haffner et al., 1989
).
In accordance with the literature (Conigrave et al., 1995; Litten et al., 1995
; Sillanaukee, 1996
) the degree of alcohol consumption had a significant effect on GGT and CDT. Even in alcohol-dependent patients, low alcohol consumption of up to 60 g/day was difficult to detect and mean levels of CDT or GGT were normal if these patients had been abstinent more than 4 days before blood sampling. This result indicates again that GGT and CDT are not ideal markers in cases of low alcohol consumption. The absence of a significant correlation between alcohol consumption and MCV is probably due to the time frame of 1 month which we used for the alcohol consumption figure. In general, other studies indicate a positive correlation between the amount of alcohol consumed and MCV (Chick et al., 1981
; Tonnesen et al., 1986
).
A significant influence of age on test results was only found for MCV, but not for CDT or GGT. MCV showed significantly higher levels for older patients and lower results for younger ones. This finding is consistent with those of previous studies (Whitfield et al., 1978; Yersin et al., 1995
; Sillanaukee et al., 1998
) and indicates that MCV increases linearly with age. The finding that GGT is not affected by age contradicts other studies (Schiele et al., 1977
; Van Der Meulen et al., 1993
; Yersin et al., 1995
) showing an increasing effect of age, but supports studies showing no clear age effect for GGT. Whitfield et al. (1978) found increasing values of GGT up to the age of 50 years, with a decrease thereafter. In the study by Sillanaukee et al. (1998), the correlation of age and GGT was only just significant (P = 0.049) and weak (r = 0.06). Persson et al. (1990) failed to demonstrate an association between age and GGT in 188 teetotallers. Daeppen et al. (1998) investigated patients only up to age 35 years. Changes in GGT over a 15-year period were minor. A linear association between age and GGT is therefore still unproven. It is possible that middle-aged patients have higher GGT values than younger and older patients. In our study, the highest GGT values were obtained in patients aged 3550 years.
Our result suggesting that CDT is not significantly correlated with age is in accordance with those of Sillanaukee et al. (1998). In this latter study, a significant correlation was found between age and MCV, but not between age and CDT. The findings that both younger and older patients have higher CDT values (Yersin et al., 1995; Huseby et al., 1997
; Agelink et al., 1998
) are indirectly supported by our study. Younger and older patients showed higher CDT levels, compared to middle-aged patients, though these effects did not reach significance and therefore a clear age effect could not be proven.
In conclusion, the results of our study confirm that CDT and GGT are effective markers for alcoholism. The two important factors influencing GGT and CDT are the duration of abstinence before blood testing and quantity of alcohol consumed. Clear age effects are shown only for MCV. If the limitations of each marker are understood and taken into consideration, biological markers, especially used in combinations, are useful aids in diagnosis of alcoholism.
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ACKNOWLEDGEMENTS |
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FOOTNOTES |
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