Modification of baseline status to improve breath tests performance.

Breath tests used to evaluate carbohydrates malabsorption require baseline H 2 and CH 4 levels as low as possible. Test cancellation is recommended when exceeding certain cut-offs (H 2  ≥ 20 ppm and CH 4  ≥ 10 ppm). Although following preparation protocols, many patients have baseline levels above those cut-offs. We investigated if light walking can reduce baseline H 2 and CH 4 levels. We retrospectively analyzed baseline H 2 and CH 4 levels from 1552 breath tests. Baseline levels (B1), especially in H 2 , were lower when obtained at later hours of the day. In those with baseline levels above cut-off, re-sampling (B2) after light walking for one hour, decreased H 2 levels 8 ppm (Q1-Q3: 1-18 ppm), and 2 ppm (Q1-Q3: 0-3 ppm) for CH 4 . Consequently, 40% of tests with elevated B1 levels, presented B2 levels below mentioned cut-offs. Ten percent of tests considered negative when using B1 for calculations, turned positive when using B2 instead. All positive tests when using B1 values, remained elevated when using B2. Re-sampling after light walking for one hour could allow test performance in those with previous elevated baseline levels, avoiding diagnosis delays. Using the second sample for delta calculations identifies positive patients for malabsorption that would have been considered negative.