The Consistency of 13C Phenylalaline Breath Test in Healthy Taiwanese Volunteers

Abstract

Background and Purpose: 13C-phenylalanine breath test was designed to estimate the phenylalanine hydroxylase activity by detecting 13CO2 production in the breath samples after ingestion of labeled 13C-phenylalanine. There were several reports that it correlated well with the liver functions and prognosis of patients. Since there is still no report about the consistency for 13C-PBT, we designed this study to test its consistency in healthy volunteers. Method: We enrolled 13 healthy adult volunteers to receive twice 13C-phenylalanine breath test within 2 weeks. After an overnight fast, they ingested 100 mg L-[1-13C] phenylalanine in 50 ml water and then breath samples were collected at baseline and then with 10 minute interval till 1 hour, then 30 minute interval to 2 hours. These samples are assayed with Infra Red Isotope Analyzer. We calculated the oxidation rate of 13C-phenylalanine and its cumulative excretion percentage at each time point and compared the data of the first and second tests obtained from the same person with Spearman coefficient test. Results: The Spearman coefficients of the first and second tests for the oxidation rate were r=-0.044, -0.239, 0.478, 0.231, 0.374, 0.346, 0.132, 0.747 at 10, 20, 30, 40, 50, 60, 90 & 120 minutes respectively; for the cumulative excretion percentage, r=-0.044, -0.159, -0.11, 0.038, 0.082, 0.11, 0.38, 0.099 at 10, 20, 30, 40, 50, 60, 90 & 120 minutes respectively. The correlations were all not good. Conclusions: Our small pilot study demonstrated that the consistency of 13C-PBT, either for phenylalanine oxidation rate or cumulative excretion percentage, were not good except for the hydroxylation rate at 120 minutes in healthy Taiwanese volunteers. More studies are needed to clarify this issue.