13C‐methacetin breath test and oxygen supply

Sirs, We read with interest the paper published by Zipprich et al. in a recent issue of Alimentary Pharmacology & Therapeutics.1 They showed that oxygen supplementation increased liver oxidation capability in cirrhotic patients in different Child classes. The cumulative dose of a 13C-methacetin breath test performed during oxygen transnasal inhalation (4 L/min) was significantly higher than that obtained in basal conditions (room air). The authors stated that the impact of oxygen supplementation on microsomal liver activity was similar in different stages of liver dysfunction, thus suggesting that oxygen susceptibility of the cirrhotic liver is an early event during the course of the disease. It would be interesting to perform a similar study on healthy subjects to clarify whether oxygen supplementation may influence the results of the 13C-methacetin breath test in ‘normal liver’. The effect of oxygen supplementation on the 13C-methacetin breath test could influence metabolic factors (e.g. interference with the bicarbonate central body pool and increased excretion of CO2) other than liver microsomal activity.