Biokinetics and radiation doses for carbon-14 urea in adults and children undergoing the Helicobacter pylori breath test

The long-term biokinetics and dosimetry of carbon-14 were studied in nine a dults and eight children undergoing carbon-14 urea breath test for Helicoba cter pylori (HP) infection. The elimination of C-14 via exhaled air and uri ne was measured with the liquid scintillation counting technique and with a ccelerator mass spectrometry. After the subjects had been given 110 kBq C-1 4-urea (children: 55 kBq) orally, samples of exhaled air were taken up to 1 80 days after administration and samples of urine were collected up to 40 d ays. Sixteen of the subjects were found to be HP-negative. In these subject s a total of 91.1%+/-3.9% (mean of adults and children +/- standard error o f the mean) of the administered C-14 activity was recovered. The majority o f the administered activity, 88.3%+/-6.2% in adults and 87.7%+/-5.0% in chi ldren, was excreted via the urine within 72 h after administration. A small er fraction was exhaled. In adults 4.6%+/-0.6% of the activity was exhaled within 20 days and in children 2.6%+/-0.3%. Uncertainties in the biokinetic results are mainly due to assumptions concerning endogenous CO2 production and urinary excretion rate and are estimated to be less than 30%. The abso rbed dose to various organs and the effective dose were calculated using th e ICRP model for urea and CO2. The urinary bladder received the highest abs orbed dose: in adults, 0.15+/-0.01 mGy/MBq and in children of various ages (7-14 years), 0.14-0.36 mGy/MBq. The findings indicate that an investigatio n with C-14-urea gives an effective dose to adults of 2.1+/-0.1 mu Sv (for 110 kBq) and to children of 0.9-2.5 mu Sv (for 55 kBq). From a radiation pr otection point of view, there is thus no reason for restrictions on even re peated screening investigations with C-14-urea in whole families, including children.