Breath tests with stable isotopes: have they a role in liver transplantation?

Evaluation of liver function is crucial in the overall management of patients with liver disease. In particular, patients with end-stage liver disease need accurate prognostic indicators to plan liver transplantation, and in this case, to manage their presence in the waiting list. Availability of predictors of clinical outcome is further essential after liver transplant, mainly to correctly diagnose and adequately treat complications, such as acute rejection, drug toxicity, liver dysfunction. Breath tests using labelled substrates selectively metabolized within the liver may represent an accurate diagnostic and prognostic tool in these clinical conditions, possibly with an adjuntive role to the most commonly used prognostic models (Child-Pugh and MELD scores). Promising results have been in fact recently obtained by the use of different substrates (aminopyrine, methacetin, erythromycin, methionine) which explore different metabolic function of the hepatocyte. The usefulness of breath tests has been documented in liver disease patients both before and after liver transplantation, in the early as well as in the late phase.