Breath hydrogen excretion or plasma acetate levels during the lactulose tolerance test?

Since both acetate and hydrogen are produced by colonic bacterial fermentation, the clinical utility of the measurement of either parameter in nine subjects for the lactulose tolerance test was tested. The fasting plasma acetate concentration (mean +/- s.d., mmol/l) of 0.11 +/- 0.06 increased to peak levels between 150 min (0.23 +/- 0.12) and 180 min (0.23 +/- 0.09), both P less than 0.01, after ingesting 20 g lactulose. In one subject with previous gastrectomy and intestinal hurry, the peak was at 30 min. Mean post-lactulose acetate levels (0.21 +/- 0.09) were higher than fasting levels (P less than 0.03). Breath hydrogen excretion exhibited a similar trend. Indeed, a significant correlation (rs 0.39, P less than 0.01) was demonstrated between the acetate and hydrogen values. It is therefore concluded that patients for the lactulose breath test show fairly similar changes in plasma acetate and breath hydrogen excretion after lactulose ingestion. Either measurement could thus be used in assessing colonic fermentation in humans.