Caffeine Breath Test Measures Liver Function

Forget the liver biopsy. Now it's possible to detect advanced fibrosis - a complication of many liver diseases including hepatitis B, hepatitis C, fatty liver disease and hemochromatosis - by means of a simple breath test.

An Australian research team has developed the test, which involves drinking a small quantity of caffeine tagged with a short-lived isotope of carbon, and then blowing into a test tube one hour later.

The test can be conducted in an outpatient setting, so patients don't need to take time off work for a long procedure.

Describing the test at Australian Gastroenterology Week 2004, Dr. Gordon Park, a gastroenterologist at Concord Hospital in Sydney, said the test is "a promising method of assessing the severity of liver disease and monitoring a patient's response to treatment."

Caffeine was selected for the test because it is metabolized exclusively through the liver, he said. "An enzyme in the liver breaks it down, and the ability of that enzyme to break it down is intimately related to overall liver function."

The carbon isotope incorporated into the caffeine is eventually expelled in the breath as carbon dioxide. Because the isotope is slightly radioactive, the amount of it can be easily measured

"If the liver is not functioning well, metabolism of caffeine is impaired," Parks explained, and the amount of carbon isotope in the breath is reduced.

Cigarette smoking is a major confounder of the test in that it increases the activity of the liver enzyme, Park commented. Smokers generally have double the normal activity of nonsmokers.

"We can factor that into the analysis, and we have already done studies looking specifically at smokers," Park said. "We have now formulated a reference range for smokers and for nonsmokers."