Urinary fluoride reference values determined by a fluoride ion selective electrode

As fluoride has a very short half-life in the body and the major route for fluoride excretion is via the kidney, human exposure is best measured in urine, where the concentration is expected to be highest. The urinary fluoride concentrations of 167 healthy Japanese adults were determined by means of a fluoride ion selective electrode. When the results were corrected for a specific gravity rho = 1.024 g cm-3, the histogram of urinary fluoride concentrations highly skewed toward low values with sharp peakedness (skewness = 1.56, kurtosis = 3.08). The normality of the log-transformed histogram (skewness = 0.12, kurtosis = 0.07) and the straight line on log-probability paper clearly showed a key feature of lognormal distribution of urinary fluoride. A geometric mean (GM) of 613.8 microg/l and 95% confidential interval (CI) of 241.0-1633.1 microg/l were established as reference values for urinary fluoride. The results presented in this study will be useful as guidelines for the biological monitoring of fluoride in normal subjects and individuals at risk of occupational or environmental fluoride exposure.