The purpose of this study is to evaluate the feasibility and validity of the breath test with L-[1-13C]phenylalanine orally administrated in assessing liver function quantitatively. L-[1-13C]phenylalanine breath tests were performed in 10 patients with compensated liver cirrhosis

10 patients with decompensated liver cirrhosis and 10 normal subjects. Breath samples were taken before oral administration and at different time intervals within 360 minutes after administration of L-[1-13C]phenylalanine (100mg / case) and the enrichment of breath 13CO2 was measured by an isotope ratio mass spectrometer. The percentage of 13C excretion rate at 30 minute (13CO2ER30) and the percentage of 13C cumulative excretion within 75 minutes (13Ccum75) were studied among the above groups and were compared to clinical liver function tests. Result showed that 13CO2ER30 were 7.4% 13C dose/h ?.0% 13C dose/h and 3.5% 13C dose/h ?.1% 13C dose/h in patients with compensated liver cirrhosis and patients with decompensated liver cirrhosis

both were significantly lower than that of normal subjects (12.1% 13C dose/h 2.1% 13C dose/h

P<0.001

respectively). 13Ccum75 were 7.0% 13C dose ?.1% 13C dose and 3.8 13C dose ?.0% 13C dose in patients with compensated liver cirrhosis and patients with decompensated liver cirrhosis

and both were also significantly lower than that of normal subjects (10.6% 13C dose ?.6% 13C dose

P<0.001

respectively). These two parameters signifi-cantly correlated with some clinical liver function tests (P<0.05). The present results seem to indicate that oral L-[1-13C]phenylalanine breath test is a simple

sensitive

specific and quantitative test for the measurement of instant liver function

whereas 13CO2ER30 and 13Ccum75 are two useful parameters for evaluation.