The use of stable isotopes is meant to allow a more pathophysiological approach to liver disease by using a battery of breath tests that examine the integrity of different metabolic pathways. Several tests are being investigated. These are:¹³C aminopyrine breath test (ABT),1 ¹³C methacetin breath test (in both of which the substrate is metabolised by the cytochrome P450 enzyme system), ¹³C phenylalanine breath test (PBT), and, finally, ¹³C galactose breath test (GBT).

The galactose elimination capacity (GEC) test was proposed several years ago as a quantitative test to measure liver function.2 However, the multiple blood samples needed to establish the decrease of galactose concentration make the test difficult in clinical practice and has led to the investigation of the possible use of a [1-¹³C] GBT in the management of chronic liver diseases.

The metabolism of galactose occurs via a cytosolic pathway independent of the cytochrome P450 system. Thus, there is less variation of its metabolism due to drug induction or inhibition, or genetic polymorphism. The fact that this carbohydrate has a high extraction ratio, however, makes the metabolism of galactose dependent on liver blood flow and hepatic functional mass. To overcome this problem the metabolic pathway must be saturated by giving a large dose of galactose: in this case, its metabolism is directly correlated to the hepatic functional mass.3-6

Theoretically, a combination of breath tests (using galactose and aminopyrine, for example) will enable the investigation of total liver functional capacity, and would be applicable in the prognosis of liver disease and also in the follow up assessment of liver transplant patients.

In abstract 1 the GBT (after intravenous substrate administration) is compared with the classic GEC test in controls and patients with liver disease. Good correlation was obtained in all …