Scrutiny of 13C-phenylalanine breath test reproducibility.

We evaluated the reproducibility of the 13C-phenylalanine breath test (13C-PheBT). On three separate days, 21 healthy volunteers (11 F and 10 M) underwent 13C-PheBT with 100 mg l-[1-13C]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 13C-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 13C recovery area under the curve (AUC) offers much better reproducibility than the maximum momentary 13C recovery in the expiratory air (Dmax) or the time to reach the maximum momentary 13C 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 13C-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 13C-PheBT is worse than either that of of the 13C-methacetin (13C-MBT) or the 13C-alpha-ketoisocaproic acic (13C-KICA-BT) breath tests. This finding will have to be taken into consideration while interpreting the results of this diagnostic tool.