Lab test offers new way to spot alcoholism

A recently approved blood test could aid efforts to screen and treat alcohol addiction.

By Victoria Stagg Elliott, amednews staff. Aug. 28, 2000.

The first Food and Drug Administration-approved lab test using biochemical markers to diagnose alcohol abuse holds promise as an aid in screening for alcoholism. It may also help addiction medicine specialists diagnose relapse long before their patients will admit to it, experts say.

The carbohydrate-deficient transferrin test received FDA approval in May and will be launched commercially later this year.

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Biochemical tests -- particularly gamma glutamyl transferase, which gauges liver damage -- have long been used to determine the physical impact of consuming large amounts of alcohol. GGT, however, has never been very useful or conclusive for alcoholism diagnosis because liver damage can be caused by a variety of factors. The new test could lead to more insights.

"There are very few conditions that can elevate CDT other than excessive drinking, and those conditions are rare," said John Allen, PhD, associate director of treatment studies at the National Institute on Alcohol Abuse and Alcoholism.

Doctors working with patients who abuse alcohol say the concrete numbers the test provides will help them overcome the biggest barrier to caring for such patients: denial that there is a problem.

"One of the utilities of a lab test is that it does make an impression on some people," said Robert Niven, MD, medical director of Brighton (Mich.) Hospital, an alcohol and drug addiction treatment facility. "It helps break through the denial and the rationalization. There are still some people who will say, 'You've got a bad lab,' or 'It's not my blood.' But for many people it is helpful."

Addiction medicine specialists warn, however, that although CDT will be a useful tool, it is not in itself a conclusive test for alcoholism. Although it results in fewer false-positives than the GGT, it still does result in a significant number of false-negatives, particularly in women, who tend to drink less than men.

"It's not an 'Aha!' type of test where you look at it and you've got it," said Dr. Niven. "And when it's negative, it doesn't rule out alcoholism, and that's really important to understand. ... Good diagnostic interviewing along with laboratory screening ends up making a good diagnosis or ruling it out."

Treatment experts say that when CDT is on the market, it will probably be used in conjunction with GGT.

"The important thing is that if you use the tests in combination, you significantly improve the sensitivity and pick up a bunch of new cases," said Dr. Allen. "In the case of women, that is even more important, because the tests are less sensitive in females, so using them together makes even more sense."

For a CDT test to be positive, a patient would have to consume at least 3.5 standard drinks a day -- roughly five glasses of beer or four glasses of wine -- for one to two weeks. There is also evidence that long-time abusers who relapse will show up positive after much less drinking. Experts say that people can be alcoholics and drink much less than that.

"None of the markers are perfect, so constantly developing new markers is important," said Dr. Allen, who participated in a discussion comparing biochemical tests at the annual meeting of the American Assn. for Clinical Chemistry last month. The attendees endorsed CDT as the most specific and useful of the tests.

Those who work with alcoholics say that although the CDT test will be very helpful to primary care physicians as a screening tool, it will be even more useful to addiction medicine specialists looking for signs of recurrent drinking. The reason is that CDT is more specific and more sensitive than GGT to sudden spikes in alcohol consumption.

"Where I see the real value of the test is for those patients who are at high risk for relapsing but are very reluctant, as many of our patients are, to disclose that," said Daniel Hall-Flavin, MD, director of addiction services at the Mayo Clinic in Rochester, Minn. "It's kind of a safety net."

He estimated that he would be able to intervene in relapsed patients four to five weeks sooner than he would if he waited until they disclosed voluntarily that that they were drinking again. "That four or five weeks can be critical for some," he said.