0145-6008/94/1803-0653$3.00/0 ALCOHOLISM: CLINICAL AND EXPERIMENTAL RESEARCH

Vol. 18, No. 3 May/June 1994

A Correlational Study of Carbohydrate-Deficient Transferrin Values and Alcohol Consumption among

Hispanic College Students Linda La Grange, Raymond F. Anton, Hal Crow, and Susan Garcia

One hundred and forty-eight US. college students from a small southwestern university were asked to provide or complete the following: the Michigan Alcoholism Screening Test (MAST), a struc- tured alcohol-use interview, and a 10-mI blood sample to be assayed for carbohydrate-deficient transferrin (CDT) levels and y-glutamyl- transpeptidase (GGTP) activity. Using the data obtained in the inter- view, only 2 females and 5 males were identified as heavy drinkers. Conclusions regarding the efficacy of the biochemical markers are therefore limited. It was found that CDT levels were significantly and positively correlated with various measures of alcohol consumption among males. There was no similar association between CDT, or GGTP, and alcohol consumption within the female sample.

Key Words: Carbohydrate-Deficient Transferrin, y-Glutamyltrans- peptidase, Biological Marker, Alcoholism.

OR THE PAST several years, researchers have noted F that a fraction of the serum transfemn of alcoholics, when analyzed by isoelectric focusing (PI), appears above a PI of 5.7,’ whereas most “normal” transfemn has a PI of 5.2-5.7.2 The composition of this abnormal transfemn is characterized by lower concentrations of sialic acid, galactose, and N-acetylgluc~samine.~ Researchers have since conducted a series of studies investigating the possi- bility that carbohydrate-deficient transfemn (CDT) might be of value as a marker of excessive alcohol consumption. Thus far, indications are that the use of CDT as such a marker can yield predictive values of -94%, at least within a male alcoholic p~pulat ion.~-~ The usefulness of CDT as a marker is, however, not confirmed among young adults, particularly females. In a recent Finnish study of college- aged students, the value of CDT as a marker of alcohol consumption was quite When data were analyzed by gender, the usefulness of CDT was further reduced among females.

Unfortunately, data from most investigations of possible biological markers of excessive alcohol consumption have

From the Department of Psychology (L.L.. S.G.), New Mexico High- lands University, Las Vegas, New Mexico; and the Medical University of South Carolina (R.F.A., H.C.), Charleston, South Carolina.

Received for publication June 7, 1993; accepted September 29, 1993 This work was supported by a grant from the National Institute on

Alcohol Abuse and Alcoholism (R03 AAO8582-02). Reprint requests: Linda La Grange, Ph.D.. Associate Professor of

Psychology, Department of Psychology, New Mexico Highlands Univer- sity, Las Vegas, NM 87701.

Alcohol CIin Exp Res, Vol 18, No 3, 1994: pp 653-656

Copyright 0 I994 by The Research Society on Alcoholism.

been obtained from males. Yet young adult females, when pregnant, constitute the only population in which the excessive consumption of alcohol has the potential to directly harm two organisms: mother and fetus. As well, the adverse physiological consequences, such as liver dam- age, appear earlier, and with more severity, in females than in males. It is within this female population that we are seeking to establish the efficacy of CDT as a marker of heavy alcohol consumption. In addition, we are at- tempting to establish baseline levels of CDT for both genders in a young adult Hispanic population.

MATERIALS AND METHODS

Study Po~ulaiion

Volunteers for this study were recruited from Psychology 101 classes in a small southwestern university. Extra course credit was given to all participants. Data collection procedures were approved by the university IRB, and each participant read and signed an informed consent form prior to participation. University demographics reflect a racial/ethnic distribution of 68% Hispanic, 2 1 % White, and 1 1 % Native American, African-American, and Asian. There were 44 males whose mean age was 25.5, with a range of 18-45 years, and 104 females with a mean age of 23.7 and a range of 18-49 years. The interviews and blood draw were conducted in one session. All sessions were held between 9:OO AM and 12:OO noon.

Determination of Alcohol Consumption

The structured interview format was adapted from Waterson and

Murray-Lyon.R The interview consisted of the following questions: 1. 2.

3. 4.

5.

6 .

I .

Do you ever drink wine, beer, or liquor? How many cans of beer, glasses of wine, or mixed drinks can you consume before you start to feel high? How often do you drink wine, beer, or liquor a week? How many drinks (specify wine, beer, or liquor) do you consume on each occasion? How often do you have as much as 9 beers, 9 mixed drinks, 2 bottles of wine, or 1 bottle of sherry in one day? a. Never b. Less than once a month c. Once a month d. Once a week Have you at any time during the last 30 days taken any prescribed medication (including oral contraceptives)? If SO, what was the drug? Have you at any time during the last 30 days used any drugs (i.e., marijuana, cocaine, amphetamine, heroin, etc.) recreationally? If so, what was the drug?

653

654 LAGRANGE ET AL.

8. How many days has it been since the onset of your last menstrual period?

9. Are you pregnant?

The answers to questions 2 and 4 were converted to standard drinking units (SDUs), where one SDU is equal to 0.5 oz of absolute ethanol. To allow for a direct comparison with the Nystrom et al.' study, consump tion levels were computed in kg/year of absolute ethanol. In addition to the structured interview, subjects completed the Michigan Alcoholism Screening Test (MAST).9

Determination of CDT in Serum

After collection and separation, blood samples were kept frozen at -8o'C. The assay was performed at The Institute of Psychiatry, Medical University of South Carolina, using a kit marketed by Pharmacia, whose general method and validity have been previously described.l0 The procedure is a double antibody radioimmunoassay that begins with the separation in disposable columns of the different isoforms of the trans- femn. CDT collected in the elute competes with a known amount of '251-labeled transfemn for binding sites on the antibodies. A second immunoadsorbent antibody is added that separates the bound and free transfemn. The mixture is centrifuged and the supernatant discarded. The radioactivity in the pellet is then measured and is inversely related to the amount of CDT present in the sample, as determined by standard curves of authentic CDT, and is reported in unitsbiter.

Determination of y-Glutamyltranspeptidase (GGTP) in Serum

After collection, blood samples were frozen at -80°C. Serum GGTP activity was determined via the kinetic method." Using y-glutamyl-p nitroaniline (0.44 mM) as the substrate and glycylglycine (92 mM) as a glutamyl residue acceptor, the rate of pnitroaniline formation was meas- ured with a spectrophotometer at 410 nm. One unit of activity (units/ liter) is expressed as that amount of GGTP necessary to liberate 1 p~ p- nitroaniline from the substrate/min at 37°C. The reaction was initiated by the application of the substrate and terminated by adding 10% trichloroacetic acid.

Statistical Analysis

The statistical analysis was conducted using the BMDP Statistical Software Package. Program 5D was run to determine the descriptive statistics and provide a graphic display of the distribution for each variable. To assess the strength of the correlation between each of the two biochemical markers of alcohol consumption and self-reported levels of alcohol consumption, the Pearson's r, as computed by Program 6R, was used.

RESULTS

Among females, 6.7 % were complete alcohol abstainers, as were 4.5% of the males. Of those exceeding a consump tion level of 16 kg/year, 2% were females and 1 1 ?6 were male. Alcohol consumption for females averaged 195 SDUs (2 kg)/year, and males consumed an average of 420.61 SDUs ( 5 kg)/year. Females, therefore, had mean daily consumption levels of 6 g and males averaged 14 g per day.

Nystrom et al.' found that, among college-age males, the mean CDT value was 13.3 units/liter and among females, 18.2 units/liter. As indicated in Table 1, the values for our study sample were quite similar. As has been the case in previous studies, * values for females were

Table 1. Serum CDT Values for Southwest U.S. College Students

Group

CDT (unitspiter) % Exceeding

26 unitspiter, females n Mean SD 20 units/liter, males

Female students All Teetotalers Social drinkers Heavy drinkers

Male students All Teetotalers Social drinkers Heavy drinkers

104 16.6 6.0 7 15.1 3.2

95 16.5 5.6 2 21.5 8.1

44 13.9 4.8 2 13.7 3.9

37 13.2 3.2 5 14.9 5.5

1 .o 0.0 0.0

50.0

11.0 0.0

10.8 20.0

Note: Heavy drinkers consumed at least 16 kg/year.

T a m 2. Serum GGTP Values for Southwest U.S. College Students GGTP

(unitspter) % Exceeding 36 units/liter, females

Group n Mean SD 55 units/liter. males Female students

All Teetotalers Social drinkers Heavy drinkers

Male students All Teetotalers Social drinkers Heavy drinkers

75 23.7 12.8 2 20.4 10.4

71 23.0 11.5 2 27.6 19.4

36 39.6 20.1 2 36.1 39.4

29 37.3 24.1 5 45.5 19.7

14.0 0.0

14.4 50.0

27.0 50.0 27.1 40.0

Note: Heavy drinkers consumed at least 16 kglyear.

Table 3. Correlations Between CDT, GGTP, and Drinking Measures ~~

CDT GGTP ~

Males Females Males Females Dnnking measures (n = 44) (n = 104) (n = 36) (n = 75)

MAST 0.362' 0.081 0.023 0.109 High 0.382' -0.048 0.052 0.056 Frequency 0.201 0.036 0.387' 0.106 Quantity 0.328' 0.072 -0.002 -0.083

Note: High = number of SDUs required to feel "high": frequency = number of drinking episodes/month: quantity = number of SDUs consumed during an average drinking episode.

* D c 0.05.

higher than those of males. The percentage of subjects whose CDT levels exceeded cutoff levels is also reported in Table 1 . Cutoff points for CDT were positioned at 26 units/liter for females and 20 units/liter for males, as recommended by Pha~macia'~ and as used by the Nystrom et al.7 study. In the current study, the CDT mean plus 2 SD was 28.6 for females and 23.5 for males, whereas in the Nystrom et al.7 study, the CDT mean f 2 SD was 30.4 for females and 22.9 for males. Normative CDT values as determined by the laboratory at which the current study's samples were assay have been established at 17 units/liter for males and 25 units/liter for females, and are docu- mented in a paper recently submitted for publication (R. Anton, personal communication) (also see Table 2).

Male CDT values were significantly correlated with 3 of the 4 drinking measures, including the number of drinks required to feel "high" and the quantity of alcohol typically consumed in a single drinking session (see Table 3). Fe-

CORRELATIONAL STUDY OF CDT VALUES 655

male data, however, were not indicative of an association between CDT values and any of the drinking measures.

There was no association between GGTP and indices of alcohol consumption among females, whereas among males there was a moderate positive correlation between frequency of drinking and GGTP activity. There are fewer subjects reported in conjunction with GGTP data than with CDT, because for a number of subjects, there was an insufficient quantity of serum to perform both the GGTP andCDT assay.

With regard to the relationship between the two biolog- ical markers, the correlation between CDT and GGTP for males was -0.05 and for females 0.17. A similar lack of association between the two biochemical variables was noted by Nystrom et al.,7 who reported correlations of 0.14 for males and -0.69 for females.

Sensitivity, specificity, and positive predictive values (PPV) were computed for both CDT and GGTP (see Table 4). The term positive is applied to subjects whose self- reported levels of alcohol consumption exceeded 16 kg/ year, whereas the term negative indicates a consumption level < 16 kg/year. Sensitivity refers to the correct associ- ation between a marker value that exceeds cutoff points and high alcohol consumption. Among males, CDT sen- sitivity was 20%, a figure similar to the 21.7% observed in the Nystrom et a1.’ study. The relatively high sensitivity level (50%) for females is not consistent with the correla- tional data obtained in the current study. We therefore assert that the small number of female heavy drinkers (2) make it impossible to attach much credence to the 50% figure.

DISCUSSION

Gjerde et aL5 noted that the use of CDT appeared superior to that of mean corpuscular volume and GGTP as an indicator of excessive alcohol consumption in a nonselected population. Bliding et al.,I4 too, observed that the sensitivity and specificity of GGTP were insufficient to be of value in detecting heavy alcohol consumption in young males. Our results partially support these observa- tions in that CDT was positively correlated with the drink- ing measures among males and was certainly a more specific marker than GGTP. The low correlation of GGTP Table 4. Sensitivity, Specificity, and PPVs in Detecting Heavy Drinking in College

Students

Sensitivity Specificity PPV 1%) 1%) (YO) . . . . . ,

Female students CDT 50.0 99.0 50.0 GGTP 50.0 70.0 04.0

CDT 20.0 89.0 20.0 GGTP 57.0 68.0 28.0

Male students

Note: Cutoff points are: CDT = 26 units/liter for female students and CDT = 20 units/liter for male students; GGTP = 36 units/liter for female students and GGTP = 52 units/liter for male students. Heavy drinking was defined as a reported consumption of at least 16 kglyear of pure ethanol.

and self-reported alcohol consumption among females is consistent with the results of a study of pregnant women15 in which GGTP sensitivity was only 25% in those females consuming >30 g of alcohol/day. Using CDT cutoff values of 26 units/liter for females and 20 units/liter for males, we found 5 (12%) males and 2 (2%) females whose CDT values exceeded those cutpoints. Of the 5 males, 1 reported consuming > 16 kg of alcohol/year. His actual annual consumption exceeded 25 kg, and his CDT levels were 24 units/liter, and GGTP was 4 1 units/liter. Among females, only 1 of the 2 CDT-positives reported consuming >16 kg/year. Both of the females with high CDT values also exceeded the cutoff point for GGTP values. Among the students consuming >16 kg/year, 1 female and 1 male had elevated values for both CDT and GGTP. Therefore, the combination of GGTP and CDT did not significantly improve the sensitivity of the tests.

There were two self-identified alcoholics in our study. One, a 44-year-old male, had been in recovery for >5 years. His CDT and GGTP values were both well within the normal range. The second, another 44-year-old male, was still drinking regularly at the time of the interview and blood draw. His CDT and GGTP values were both elevated above the normal range.

Following the recommendations of Brown,I6 we used a MAST score of 12 or more as an indication of alcohol abuse. In addition to the two self-identified alcoholics, 2 males and 1 female met the >12 MAST score criterion. Only 1 of the 5 MAST-positive subjects was completely abstaining from alcohol consumption. Examination of the data taken from the remaining four subjects revealed that 2 of the 4 had elevated CDT levels, and all 4 had elevated GGTP activity. The average age of this small group was 35.6 years, which is much older than the total group age mean of 24.6 years. As previously mentioned, Nystrom et al.’ and Bliding et al.14 have indicated that biochemical markers of alcohol consumption appear to lack sensitivity and specificity when used in young adults. We have found this to be the case with our student population, where neither GGTP nor CDT were particularly useful as bio- logical markers in females. It is our conclusion, based on our small sample of southwestern U.S. college students, that CDT, because of its robust correlation with drinking measures, may be of value as a biological marker for early heavy drinking among males. However, among young females, neither CDT nor GGTP seemed strongly associ- ated with heavy alcohol consumption.

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