| The Reproducibility of 109Cd-based X-ray Fluorescence Measurements of Bone Lead Chris L. Gordon,
1
Colin E. Webber,
1
and David R. Chettle
2
1
Department of Nuclear Medicine, Chedoke-McMaster Hospitals, and
2
Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8N 3Z5 Canada
Abstract
We assessed the reproducibility of X-ray fluorescence-based lead measurements from multiple measurements made on a low-concentration plaster of paris phantom and in five subjects measured five times on two occasions. Over a 6-month period, 220 measurements of the same phantom were obtained and showed a standard deviation of 1.29 µg Pb (g plaster of paris) -1 . The two sets of in vivo measurements were made 10 months apart and revealed a mean standard deviation of 3.4 µg Pb (g bone mineral) -1 and 5.1 µg Pb (g bone mineral) -1 for males and females, respectively. Our measured standard deviation exceeded by 20-30% the calculated standard deviation associated with a single measurement both in the phantom and in subjects. This indicates that some variance is introduced during the measurement process. Operator learning and consistency significantly minimized this increased variability. Measured lead concentrations of the left and right tibia in 14 subjects showed no significant differences between legs. As a result, either tibia can be sampled and compared over time. The levels of reproducibility we report here mean that X-ray fluorescence-based determinations of bone lead concentrations are reliable both over the short and long term. Thus, reasonably sized confidence intervals can be placed on detected changes in concentration and should permit acquisition of longitudinal data within a reasonable length of time. Key words: bone lead, reproducibility, X-ray fluorescence. Environ Health Perspect 102:690-694 (1994) Address correspondence to C.L. Gordon, Department of Nuclear Medicine, Chedoke-McMaster Hospitals, 1200 Main Street West, Hamilton, Ontario, L8N 3Z5 Canada. This work was made possible by an Occupational Health and Safety Award (253/R) from the Workplace Health and Safety Agency, Ontario. Received 9 December 1993 ; accepted 19 May 1994.
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