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No radiation protection reasons for restrictions on ¹⁴C urea breath tests in children

¹ Department of Radiation Physics, Lund University, Malmö University Hospital, SE-205 02 Malmö, ² Department of Laboratory and Imaging Sciences, Malmö University College, Malmö University Hospital, SE-205 02 Malmö, ³ Department of Nuclear Physics, Lund University, Box 118, SE-221 00 Lund, ⁴ Department of Quaternary Geology, Lund University, Tornavägen 13, SE-223 63 Lund ⁵ Department of Clinical Physiology, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden

Traditional ¹⁴C urea breath tests are normally not used for younger children because the radiation exposure is unknown. High sensitivity accelerator mass spectrometry and an ultra-low amount (440 Bq) of ¹⁴C urea were therefore used both to diagnose Helicobacter pylori (HP) infection in seven children, aged 3–6 years, and to make radiation dose estimates. The activity used was 125 times lower than the amount normally used for older children and 250 times lower than that used for adults. Results were compared with previously reported biokinetic and dosimetric data for adults and older children aged 7–14 years. ¹⁴C activity concentrations in urine and exhaled air per unit administered activity for younger children (3–6 years) correspond well with those for older children (7–14 years). For a child aged 3–6 years who is HP negative, the urinary bladder wall receives the highest absorbed dose, 0.3 mGy MBq^-1. The effective dose is 0.1 mSv MBq^-1 for the 3-year-old child and 0.07 mSv MBq^-1 for the 6-year-old child. For two children, the 10 min and 20 min post-¹⁴C administration samples of exhaled air showed a significantly higher amount of ¹⁴C activity than for the rest of the children, that is 6% and 19% of administered activity exhaled per hour compared with 0.3–0.9% (mean 0.5%) of administered activity exhaled per hour indicating that these two children that is were HP positive. For a 3-year-old HP positive child, absorbed dose to the urinary bladder wall was 0.3 mGy MBq^-1 and effective dose per unit of administered activity was 0.4 mSv MBq^-1. Using 55 kBq, which is a normal amount for older children when liquid scintillation counters are used for measurement, the effective dose will be approximately 6 µSv to a 3-year-old HP negative child and 20 µSv to a HP positive child. Thus there is no reason for restrictions on performing a normal ¹⁴C urea breath test, even on young children.

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