|
|
||||||||
Articles |
-Glutamyltransferase
1
Pharmacia & Upjohn Diagnostics AB, Alcohol Related Diseases, 751 82 Uppsala, Sweden.
2
University of Tampere, Medical School and Tampere
University Hospital, Department of Clinical Chemistry, 33014 Tampere,
Finland.
3
Karolinska Institute, Medical School, 171 77 Stockholm,
Sweden.
4
Swedish University of Agricultural Sciences, Department
of Biometry and Informatics, 750 07 Uppsala, Sweden.
a Address correspondence to this author at: Oy Finnish Immunotechnology Ltd., Lenkkeilijänkatu 8, 33 520 Tampere, Finland. Fax 358-3-31387050; e-mail
Pekka.Sillanaukee{at}finnish-immunotech.com.
| Abstract |
|---|
|
|
|---|
Methods: The diagnostic values of the most frequently used
markers [carbohydrate-deficient transferrin (CDT),
-glutamyltransferase (GGT), aspartate aminotransferase, alanine
aminotransferase, and mean corpuscular volume] were studied in an
analysis of six different clinical studies (n = 1412) on alcohol
abusers and social drinkers. The purpose of the analyses was to
determine whether a combination of markers would improve the diagnosis
of subjects.
Results: Discrimination between alcohol abusers and social
drinkers, as measured by the areas under nonparametric ROC plots, was
significantly better (P <0.001) for the new combined
marker [
-CDT = 0.8 · ln(GGT) + 1.3 · ln(CDT)] than
for any of the separate markers or combination of CDT or GGT with other
markers. The cutoff values for
-CDT (6.5) can be taken to be the
same among males and females.
Conclusions: The combined variable
-CDT is a powerful tool to
discriminate alcohol abusers from social drinkers and is recommended
for clinical use.
| Introduction |
|---|
|
|
|---|
Unfortunately, an optimal marker of excessive drinking has not been
found, either for men or for women.
-Glutamyltransferase
(GGT),1
the most widely used marker, has a sensitivity of 3485%
(6)(7)(8) but a relatively low specificity. Increased GGT
concentrations are also caused, e.g., by nonalcoholic liver disease,
most hepatobiliary disorders, obesity, diabetes mellitus,
hypertriglyceridemia, and the use of liver microsome-inducing drugs
(6)(8)(9)(10). Carbohydrate-deficient transferrin
(CDT) is a new marker for high alcohol consumption with a reported
sensitivity of 3191% and a high specificity
(6)(7)(11)(12). False
positives have been reported in patients with inborn errors of
glycoprotein metabolism, the genetic D-variant of transferrin, severe
nonalcoholic liver diseases such as primary biliary cirrhosis, and
diseases with high total transferrin (12)(13)(14)(15). In addition
to GGT and CDT, aspartate aminotransferase (ASAT) and alanine
aminotransferase (ALAT) as well as erythrocyte mean corpuscular volume
(MCV) are frequently used as markers for alcohol abuse (6).
Diagnosis of alcohol abuse using a combination of different routine laboratory markers may be valuable. Combinations of more than one marker of alcohol abuse are known to give better sensitivity but usually reduced specificity in diagnosing alcohol abuse. Discriminant analysis is a statistical tool that may be applied to a set of markers and may improve the classification power above that of any single variable, thus improving the final discrimination [see, e.g., Refs. (16)(17)(18)(19)(20)].
The primary aims of the analyses presented in this report were (a) to find laboratory variables and a combination of them that can discriminate between well-characterized subjects who are "alcohol abusers" and "social drinkers", and (b) to demonstrate that the model is clinically easy to accept.
| Materials and Methods |
|---|
|
|
|---|
Study 1 included 79 patients (20 females and 59 males) who consumed high amounts of alcohol (>60 g/day) for at least 1 week prior to blood sampling and 108 healthy subjects (60 females and 48 males) who consumed low amounts of alcohol.
Study 2 included 55 alcoholics (8 females and 47 males) who had abstained <3 days prior to sampling. All of them had drunk >80 g/day during the 2 months prior to sampling. Controls were 34 social drinkers (16 females and 18 males) who had consumed <15 g of alcohol/day.
Study 3 included 51 actively drinking alcoholics (23 females and 28 males; alcohol consumption >80 g/day). A group of 62 blood donors (32 females and 30 males) who had consumed <40 g of alcohol/day were used as controls.
Study 4 included 202 (46 females and 156 males) alcohol-dependent inpatients (as diagnosed according to DSM-III-R) and 94 (45 females and 49 males) healthy controls, of whom 83 (42 females and 41 males) consumed 020 g of alcohol/day and 11 (3 females and 8 males) consumed 2060 g/day.
Study 5 included 59 alcoholics (12 females and 47 males) who consumed >60 g of alcohol/day for at least 1 week prior to blood sampling and 299 healthy university students (194 females ad 105 males) who consumed <30 g of alcohol/day as controls.
Study 6 included 26 male alcoholics who consumed >80 g of alcohol/day. The controls were 343 healthy volunteers (165 females and 178 males) who consumed <20 g of alcohol/day.
methods
Serum CDT concentrations were analyzed by a double antibody assay
(CDTectTM; AXIS-SHIELD, Oslo, Norway). GGT, ASAT, and ALAT
were analyzed in serum samples, and MCV was analyzed in whole blood by
routine clinical chemistry methods.
statistical methods
Discriminant analysis [see, e.g., Ref. (22)] was used
to find a diagnostic rule based on the biochemical markers that could
differentiate as well as possible between alcohol abusers and social
drinkers. A stepwise selection procedure was applied to the calibration
data set to derive the best combination of markers and to eliminate
redundant information provided for different markers. Scrutiny of the
data indicated that the variances might be different in the different
groups. Therefore, the discriminant analysis was done allowing for
variance heterogeneity (22).
Variables were tested both nontransformed and in logarithmic form. Standard diagnostic methods for linear statistical models (23) suggested that CDT, GGT, ASAT, and ALAT should be analyzed in logarithmic form. The natural logarithm was used. The SAS procedures Stepdisc and Discrim (24) were used for the analyses.
Two of the data sets (studies 1 and 2) were used for calibration, i.e., for building predictive statistical models, and the remaining four data sets (studies 36) were used as validation data sets to confirm the findings from the calibration data sets.
For comparisons between different classification criteria, nonparametric ROC plots [see, e.g., Ref. (25)] were prepared. The ROC plots were prepared through a program written by one of the authors (U.O.), using the SAS language (24) and SAS/Graph plots. As summaries of the ROC plots, the area under the curve was calculated for each criterion. The area under the ROC plot can be interpreted as the probability that a randomly selected alcohol abuser has a value for a marker higher than that of a randomly selected person in the control group. Significance tests comparing the areas under nonparametric ROC plots for different markers were done using the method of DeLong et al. (26).
Results were expressed as the mean (SD) for all variables.
| Results |
|---|
|
|
|---|
|
stepwise analysis
The calibration analysis used data from studies 1 and 2, which
included a total of 276 individuals, 134 alcohol abusers, and 142
social drinkers. The purpose of this analysis was to find those
variables among the markers CDT, GGT, ASAT, ALAT, and MCV that best
differentiated between the group with high alcohol consumption and a
control group. Because there may be sex differences and differences
among the studies, dummy binary variables for sex and study were
included.
The stepwise analysis revealed that the natural logarithm transformations of CDT [ln(CDT)] and GGT [ln(GGT)] were the best predictor variables for differentiating between alcoholics and social drinkers; these variables accounted for r2 = 77.8% of all variation. The next variable, [ln(ALAT)], although formally significant, added only 2.8% explained variation. To keep the model simple, we chose to retain only ln(GGT) and ln(CDT) in the model. Neither sex nor the study effect was significant.
predictive model
The stepwise procedure did not supply coefficients for the
discriminant function. Therefore, the calibration data were analyzed
using discriminant analysis to obtain a predictive model. This analysis
gave the following discriminant function: y =
0.8 · ln(GGT) + 1.3 · ln(CDT).
cutoff limit
On the basis of earlier studies (6), recommended cutoff
limits in different study populations have been suggested to be as
follows: for males, 20 units/L for CDT [ln(CDT) = 3.00] and 40
U/L for GGT [ln(GGT) = 3.69]; for females, 26 units/L for CDT
[ln(CDT) = 3.26] and 30 U/L for GGT [ln(GGT) = 3.40]. In
our control groups, this corresponds to percentiles 92.4 (CDT, males),
98.5 (GGT, males), 94.7 (CDT, females), and 96.1 (GGT, females),
respectively.
As a tentative criterion for a cutoff limit for
-CDT we chose the
95th percentile for the control groups in our data. This would give the
limit as 6.5 for females and 6.6 for males. Because the difference
between sexes was small (a t-test comparing
-CDT between
males and females gave P = 0.72), we suggest using the
same tentative limit, 6.5, for both sexes. This recommendation may have
to be modified once data for larger samples from a general population
become available.
evaluation of validation data sets
Sensitivity and specificity.
Table 2
shows the sensitivity and specificity for all data sets for the
markers CDT, GGT, and
-CDT = 0.8 · ln(GGT) +
1.3 · ln(CDT), using the cutoff limits discussed above.
|
ROC plots.
Nonparametric ROC plots were prepared separately
for males and females. The area under the curve was calculated, along
with a test comparing the areas for the different markers. These
results are given in Table 3
. The areas under the nonparametric ROC plots were largest for
-CDT for both sexes (P <0.0001).
|
| Discussion |
|---|
|
|
|---|
A statistical method such as discriminant analysis uses biochemical markers from defined groups of subjects, and produces weighting factors for tests and derives a discriminant score that minimizes within-group differences and maximizes between-group differences. The use of such an analysis, a model combining five markers (ASAT, MCV, HDL-cholesterol/total cholesterol, triglycerides and log alkaline phosphatase) gave a sensitivity of 91% and a specificity of 96% in discriminating alcoholics from social drinkers. Corresponding values were 72% and 73%, respectively, in discriminating heavy drinkers (18). Shaper et al. (27) found that a combination of GGT, HDL-cholesterol, urate, mean corpuscular hemoglobin, and lead had a discriminant value of 41% for heavy drinkers compared with 17% for the best single test, i.e., GGT. A more complex model including 10 laboratory measurements (chloride, sodium, ratio of direct to total bilirubin concentration, blood urea nitrogen, HDL, monocyte count, phosphorus, platelets, ASAT, and mean corpuscular hemoglobin) correctly identified 98% of heavy drinkers and 95% of light drinkers (28). In spite of their better performance compared with single markers, these combinations include a large number of laboratory measurements.
The aim of this study was to investigate whether diagnosis of excessive
alcohol consumption could be improved by combining a few laboratory
markers of alcohol abuse into a joint diagnostic model. The diagnostic
model was formulated using data from two studies (studies 1 and 2). It
was found that a model that included only two markers (CDT and GGT),
here called
-CDT, performed well in these two studies to
differentiate between alcohol abusers and social drinkers.
-CDT was
defined as:
![]() |
The model was tested on data from four independent studies.
Diagnostic efficiency was evaluated in two different ways: using
nonparametric ROC plots and by calculating sensitivity, specificity,
and the total error rate using clinically accepted cutpoints for CDT
and GGT. The reference and cutoff values for
-CDT were the same
(6.5) for males and females. The area under nonparametric ROC plots was
largest for
-CDT in both genders. The total error rate among males
and females was lowest for
-CDT.
In the present study, the average sensitivity and specificity for males
were, respectively, 75% and 93% for
-CDT, 58% and 94% for CDT,
and 55% and 90% for GGT. The average sensitivity and specificity for
females were, respectively, 68% and 96% for
-CDT, 40% and 94%
for CDT, and 52% and 96% for GGT. This indicates a significant
improvement in classification using only two markers.
The sensitivity and specificity values are quite similar for GGT and CDT. Many previous studies reported similar sensitivities for GGT and CDT and higher specificities for CDT (29). However, among subjects with liver disease, the specificity of the two markers is similar.
In conclusion, the new marker
-CDT clearly outperformed both CDT
and GGT for differentiating between alcohol abusers and social
drinkers.
-CDT seems to be a valuable addition to the tools for
diagnosing alcohol abuse. Because of its relative simplicity, it should
be easy to adopt into routine use. Thus,
-CDT is recommended for the
detection of alcohol abuse in settings with a high prevalence of
alcohol abuse.
| Footnotes |
|---|
-glutamyltransferase; CDT, carbohydrate-deficient transferrin; ASAT, aspartate aminotransferase; ALAT, alanine aminotransferase; and MCV, mean corpuscular volume. | References |
|---|
|
|
|---|
-glutamyltranspeptidase activity in liver disease. Gut 1972;13:702-708.
-glutamyltransferase: statistical distribution in a middle-aged male population and evaluation of alcohol habits in individuals with elevated levels. Prev Med 1980;9:108-119.[Web of Science][Medline]
[Order article via Infotrieve]
-glutamyl transferase levels in outpatient alcoholics. Alcohol Clin Exp Res 1998;22:1456-1462.[Web of Science][Medline]
[Order article via Infotrieve]
The following articles in journals at HighWire Press have cited this article:
![]() |
S. H. STEWART, G. J. CONNORS, and A. HUTSON ETHNICITY AND GAMMA-GLUTAMYLTRANSFERASE IN MEN AND WOMEN WITH ALCOHOL USE DISORDERS Alcohol Alcohol., January 1, 2007; 42(1): 24 - 27. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. HIETALA, H. KOIVISTO, P. ANTTILA, and O. NIEMELA COMPARISON OF THE COMBINED MARKER GGT-CDT AND THE CONVENTIONAL LABORATORY MARKERS OF ALCOHOL ABUSE IN HEAVY DRINKERS, MODERATE DRINKERS AND ABSTAINERS Alcohol Alcohol., September 1, 2006; 41(5): 528 - 533. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. ARADOTTIR, G. ASANOVSKA, S. GJERSS, P. HANSSON, and C. ALLING PHOSPHATIDYLETHANOL (PEth) CONCENTRATIONS IN BLOOD ARE CORRELATED TO REPORTED ALCOHOL INTAKE IN ALCOHOL-DEPENDENT PATIENTS Alcohol Alcohol., July 1, 2006; 41(4): 431 - 437. [Abstract] [Full Text] [PDF] |
||||
![]() |
B. Lumbreras-Lacarra, J. M. Ramos-Rincon, and I. Hernandez-Aguado Methodology in Diagnostic Laboratory Test Research in Clinical Chemistry and Clinical Chemistry and Laboratory Medicine Clin. Chem., March 1, 2004; 50(3): 530 - 536. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Chen, K. M. Conigrave, P. Macaskill, J. B. Whitfield, and L. Irwig COMBINING CARBOHYDRATE-DEFICIENT TRANSFERRIN AND GAMMA-GLUTAMYLTRANSFERASE TO INCREASE DIAGNOSTIC ACCURACY FOR PROBLEM DRINKING Alcohol Alcohol., November 1, 2003; 38(6): 574 - 582. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. J. Schwarz, I. Domke, A. Helander, P. M. W. Janssens, J. van Pelt, B. Springer, M. Ackenheil, K. Bernhardt, G. Weigl, and M. Soyka MULTICENTRE EVALUATION OF A NEW ASSAY FOR DETERMINATION OF CARBOHYDRATE-DEFICIENT TRANSFERRIN Alcohol Alcohol., May 1, 2003; 38(3): 270 - 275. [Abstract] [Full Text] [PDF] |
||||
![]() |
F. J. Legros, V. Nuyens, M. Baudoux, K. Zouaoui Boudjeltia, J.-L. Ruelle, J. Colicis, F. Cantraine, and J.-P. Henry Use of Capillary Zone Electrophoresis for Differentiating Excessive from Moderate Alcohol Consumption Clin. Chem., March 1, 2003; 49(3): 440 - 449. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Sillanaukee, N. Strid, P. Jousilahti, E. Vartiainen, K. Poikolainen, S. Nikkari, J. P. Allen, and H. Alho Association of self-reported diseases and health care use with commonly used laboratory markers for alcohol consumption Alcohol Alcohol., July 1, 2001; 36(4): 339 - 345. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |