Scrutiny of 13 C-phenylalanine breath test reproducibility.

We evaluated the reproducibility of the 13 C-phenylalanine breath test (13 C-PheBT). On three separate days, 21 healthy volunteers (11 F and 10 M) underwent 13 C-PheBT with 100 mg l-[1-13 C]phenylalanine taken orally. Short-term reproducibility was evaluated with paired examinations taken 3 days apart; paired examinations separated by 23 days (median) served for the medium-term reproducibility assessment. Expiratory air was sampled at 19 points throughout 3 h. Determined limited reproducibility of the 13 C-PheBT must be taken into consideration while interpreting the results of this diagnostic tool. The results of this study imply the following conclusions: (i) From among the three parameters examined, the cumulative 13 C recovery area under the curve (AUC) offers much better reproducibility than the maximum momentary 13 C recovery in the expiratory air (Dmax ) or the time to reach the maximum momentary 13 C recovery (Tmax ) (ii) Collection of the breath air samples for 2 h results in a much better reproducibility of AUC, than for 1 h only; (iii) Reproducibility of 13 C-PheBT is affected neither by the duration of the time gap between repeated tests nor by gender; (iv) Comparison with data obtained formerly reveals that reproducibility of the 13 C-PheBT is worse than either that of of the 13 C-methacetin (13 C-MBT) or the 13 C-alpha-ketoisocaproic acic (13 C-KICA-BT) breath tests. This finding will have to be taken into consideration while interpreting the results of this diagnostic tool.