Co-variation between biological markers and self-reported alcohol consumption. A two-year study of the relationship between changes in consumption and changes in the biological markers gamma-glutamyl transpeptidase (GGT) and average volume per erythrocyte (MCV) among problem drinkers.

Co-variations between self-reported alcohol consumption and the biological markers MCV (average volume per erythrocyte) and GGT (gamma-glutamyl transpeptidase) over a 2-year period were studied in a group of 84 men and 53 women recruited to out-patient treatment by advertisements in the press. Upon admission, the drinking pattern of the participants during the preceding year was registered in detail. The participants were also medically examined, and blood samples taken. All the participants were followed up by new personal interviews, medical examinations and new blood sampling after 3, 9, 25 and 21 months. For the group as a whole, alcohol consumption was significantly lower at the end of the observation period than at admission. GGT was also decreased, but not MCV. Both self-reported consumption and the values for the biological markers showed large inter-individual and intra-individual variations during the observation period. The biological markers seemed to co-vary to a limited degree with changes in reported consumption. Both GGT and MCV seemed to have a low sensitivity but a high specificity to changes in consumption. Both markers also seemed to be somewhat more useful in identifying decreases than increases in consumption. The markers GGT and MCV should be used with caution in connection with therapeutic counselling to individuals.