Modification of baseline status to improve breath tests performance
Estibaliz Alegre 1 2 , Amaia Sandúa 3 , Sofía Calleja 3 , Sara Deza 3 , Álvaro González 3 4
Breath tests used to evaluate carbohydrates malabsorption require baseline H2 and CH4 levels as low as possible. Test cancellation is recommended when exceeding certain cut-offs (H2 ≥ 20 ppm and CH4 ≥ 10 ppm). Although following preparation protocols, many patients have baseline levels above those cut-offs.
We investigated if light walking can reduce baseline H2 and CH4 levels. We retrospectively analyzed baseline H2 and CH4 levels from 1552 breath tests. Baseline levels (B1), especially in H2, 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 H2 levels 8 ppm (Q1-Q3: 1-18 ppm), and 2 ppm (Q1-Q3: 0-3 ppm) for CH4. 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.