A comparison of two methods for the evaluation of the daily urinary fluoride excretion in Romanian pre-school children

OBJECTIVE: To compare two different methods of estimating daily fluoride urinary excretion in pre-school children under stable fluoride intake conditions. DESIGN: Thirty-five healthy kindergarten children, permanent residents of Targu-Mures, Romania, where the average drinking water fluoride concentration is 0.12 mg F/L, participated on two separate occasions, when they were aged 4-6 and 5-7 years, respectively in the collection of a) a mid-morning spot urine sample and b) a 16-h time-controlled urine sampling. In case a), the ratio of concentrations of fluoride and creatinine were measured, while in case b) the rates of fluoride excretion in two separate 8-hour periods were used to estimate the 24-hour fluoride urinary excretion. RESULTS: The estimated average daily fluoride urinary excretion values (S.D.) were 0.318 (0.182) mg F/day for method a) and 0.341 (0.193) mg F/day for method b). These values were not significantly different (Mann-Whitney U test; p = 0.49). The estimated daily fluoride doses were 0.040 (0.021) and 0.043 (0.022) mg F/kg body weight/day, respectively. The latter values were not significantly different (Mann Whitney U test; p = 0.38). CONCLUSIONS: Results obtained suggest that under stable F-intake conditions the estimation of the daily fluoride urinary excretion by means of a mid-morning spot urine sample yields comparable results to those obtained with the more involved method of separate, two 8 h (16 h) time-controlled urine sampling recommended by the WHO. Use of spot urine sampling appears to be particularly useful for epidemiological studies.