Hepatic phenylalanine metabolism measured by the [13C]phenylalanine breath test.
BACKGROUND
The amino acid clearance test including phenylalanine is known to reflect liver functional reserve, which correlates with surgical outcome; however, the procedure is not clinically useful because of its laborious and time-consuming nature. This study evaluates whether phenylalanine oxidation capacity measured by a breath test could reflect liver functional reserve.


METHODS
We determined phenylalanine oxidation capacity in 42 subjects using the L-[1-13C]phenylalanine breath test (PBT). The 13CO2 breath enrichment was measured at 10-min intervals for 120 min after oral administration of 100 mg of L-[1-13C]phenylalanine. Subjects were divided into the following three groups according to their plasma retention rate of indocyanine green at 15 min (ICG R15): Group I (ICG R15 < 10%), Group II (ICG R15 10--20%), and Group III (ICG R15 > 20%). First, we determined the parameters of the phenylalanine oxidation capacity that differentiated these groups and then, using these parameters, we compared the PBT with the ICG clearance test, Child-Pugh classification score and standard liver blood tests.


RESULTS
The %13C dose h(-1) at 30 min and cumulative excretion at 80 min were significantly different among the three groups (P < 0.05). These two parameters significantly correlated with the ICG R15, Child-Pugh classification score (P < 0.0001) and results of standard liver blood tests (P < 0.05).


CONCLUSIONS
Phenylalanine oxidation capacity measured by the PBT was reduced according to the severity of liver injury assessed by the ICG clearance test, Child-Pugh classification, and standard liver blood tests. These results indicate that the PBT can be used as a noninvasive method to determine liver functional reserve.
Kobayashi
T
T
Department of Surgery, Graduate School of Medicine, University of Tokyo, Japan. ta-koba@mb.kcom.ne.jp
Kubota
K
K
Imamura
H
H
Hasegawa
K
K
Inoue
Y
Y
Takayama
T
T
Makuuchi
M
M
D000284:Administration, Oral; D000328:Adult; D000368:Aged; D001682:Biological Availability; D001944:Breath Tests; D002247:Carbon Isotopes; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007208:Indocyanine Green / Q000493:pharmacokinetics; D008099:Liver / Q000378:metabolism*; D008111:Liver Function Tests / Q000379:methods; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000493:pharmacokinetics*
D002247:Carbon Isotopes; D010649:Phenylalanine; D007208:Indocyanine Green