13C-methacetin breath test reproducibility study reveals persistent CYP1A2 stimulation on repeat examinations

Figure 1 Time course of the ¹³CO₂ content within the total pool of exhaled CO₂ after peroral administration of 75 mg ¹³C-methacetin in 20 healthy volunteers who each underwent three breath tests on separate days. Filled rectangles represent the time points at which the rise in ¹³CO₂ concentration was statistically significantly different from the baseline measurement, open rectangles stand for values not statistically different from the baseline. The values shown are mean ± SE.

Figure 2 Relationship of the reproducibility of the cumulative ¹³C recovery, expressed in terms of the coefficient of variation for paired examinations (CV_p), on the time span taken for the calculation of the area under the curve. The short-term reproducibility (open rectangles) assessment involved performance of 20 pairs of ¹³C-methacetin breath tests separated by a median 2-d break, whereas 20 pairs of examinations accomplished at a median interval of 18 d were considered for the evaluation of the medium-term reproducibility (filled rectangles). AUC: Area under the curve.

Figure 3 Bland and Altman statistics (plot of differences between pairs vs their means) of the short- (filled diamonds) and medium-term (open rectangles) reproducibility of the ¹³C-methacetin breath test. T_max: Time to reach the maximum momentary ¹³C elimination (panel A); D_max: Maximum momentary ¹³C elimination (panel B); AUC_0-60: 60-min cumulative ¹³C elimination in expiratory air (panel C). On each panel the respective borders of the 95% confidence intervals are plotted.

Figure 4 Corresponding curves of the momentary ¹³C recovery in breath air after peroral administration of 75 mg ¹³C-methacetin in 20 healthy volunteers if two examinations were taken at a median of 2 d apart (panel A) or if the examinations were separated by a median 18 d gap (panel B). Open symbols, the first administration, filled symbols, the second administration, the values shown are mean ± SE. See the text for the results of the statistical comparison of the matching D_max and AUC_0-60 values.