THE FATE OF INGESTED C-14 UREA IN THE UREA BREATH TEST FOR HELICOBACTER-PYLORI INFECTION

The metabolic fate of the radioactive carbon in the C-14-urea breath test for Helicobacter pylori was investigated in 18 subjects. After ingestion of labelled urea, breath was sampled for 24 h, and urine was collected for 3 days. Subjects were designated high or low expirers on the basis of their breath counts, and this agreed well with H. pylori serologic analyses. When given 185 or 37 kBq of C-14-urea, 51% (SD = 16%, n = 11) of the label was recovered from the breath of high expirers, and 7% (SD = 3%, n = 7) from the breath of low expirers. The mean combined urinary and breath recovery for high expirers was 86% (SD = 7%), and for low expirers it was 97% (SD = 3%). It is concluded that the long-term retention of C-14 from ingested C-14-urea is low. The results enable a more accurate estimation to be made of radiation exposure resulting from the C-14-urea breath test.