ASSESSMENT OF THE INFLUENCE OF HYDROGEN NONEXCRETION ON THE USEFULNESS OF THE HYDROGEN BREATH TEST AND LACTOSE TOLERANCE-TEST

The recognition of hydrogen nonexcretion in up to 20% of tested subjec ts and the large ethnic differences in the prevalence of lactose malab sorption make it necessary to reassess the diagnostic usefulness of th e lactose tolerance test and the hydrogen breath test. Both tests were performed in 83 consecutive patients with suspected lactose malabsorp tion who ingested 50 g lactose. On a separate day a hydrogen breath te st was performed after 25 g lactulose. The prevalence of hydrogen none xcretion was 18%. The diagnostic usefulness of hydrogen breath test wa s influenced both by the individual threshold for hydrogen excretion a nd the amount of malabsorbed lactose. In addition to baseline values, breath samples for hydrogen measurements have to be taken at 30, 60, 9 0, 180, and 240 minutes after ingestion of lactose. For the lactose to lerance test only one measurement of serum glucose at 30 minutes is ne eded in addition to the baseline measurement. The combination of both tests excludes the influence of hydrogen nonexcretion, but even if a c ombined diagnostic approach utilizing the lactose hydrogen breath test and lactose tolerance test is used, 6% of patients presenting with sy mptoms suggestive of lactose intolerance cannot be classified.