title: Is the fluoride/creatinine ratio of a spot urine sample indicative of 24-h urinary fluoride?
abstract: OBJECTIVE
  The main aim of this study was to determine how representative the fluoride/creatinine (F/Cr) ratio of a spot urinary sample is of the fluoride content of a 24-h urine sample in young children aged 12-36 months. Subsidiary objectives were to: (a) evaluate the use of 24-h urine samples in monitoring fluoride exposure and (b) estimate the retention of fluoride in very young children.
  
  
  METHODS
  Seven healthy children residing in a fluoridated area completed the study. Dietary information was obtained using a 3-day estimated food diary followed by an interview on the fourth day. Samples of foods and drinks were analysed for fluoride content. Ingestion of fluoride from toothpaste was also measured. A 24-h urine sample and a morning spot urine sample were collected from each child.
  
  
  RESULTS
  The mean age of the children was 32 months (range: 16-36 months). The mean total daily intake of fluoride was 0.71 (+/-0.41) mg or 0.05 (+/-0.02) mg/kg bodyweight, of which 37% came from the diet, the remainder being from toothpaste ingestion. None of the children used any other sources of fluoride such as fluoride tablets or fluoridated salt. The mean F/Cr ratio was 1.49 (+/-0.63) mg F/g creatinine. A positive correlation (Pearson's correlation=0.76, P=0.05) between fluoride excretion estimated using the F/Cr ratio in a morning spot urine sample and fluoride excretion in a 24-h urine sample was found. There was also a positive correlation (Pearson's correlation=0.83, P=0.02) between total daily fluoride intake and 24-h urinary fluoride excretion. Less than half (43%) of the total daily fluoride intake was retained in the body.
  
  
  CONCLUSIONS
  The F/Cr ratio of a morning spot urine sample may be used to estimate mean 24-h urinary excretion of fluoride and therefore has potential application for larger-scale epidemiological studies where 24-h samples are impractical. Estimates of 24-h urinary fluoride excretion can be used to gauge fluoride exposure.
authors.affiliation: School of Dental Sciences, University of Newcastle, Newcastle upon Tyne, UK. vida.zohoori@ncl.ac.uk
authors.forename: F V
authors.initials: FV
authors.lastname: Zohouri
authors.forename: C M
authors.initials: CM
authors.lastname: Swinbank
authors.forename: A
authors.initials: A
authors.lastname: Maguire
authors.forename: P J
authors.initials: PJ
authors.lastname: Moynihan
mesh_terms: D001628:Beverages / Q000032:analysis; D001835:Body Weight; D002327:Cariostatic Agents / Q000008:administration & dosage / Q000032:analysis*; D002675:Child, Preschool; D003404:Creatinine / Q000652:urine*; D005247:Feeding Behavior; D005260:Female; D005459:Fluorides / Q000008:administration & dosage / Q000032:analysis / Q000652:urine*; D005504:Food Analysis; D006801:Humans; D007223:Infant; D008297:Male; D010710:Phosphates / Q000032:analysis; D015203:Reproducibility of Results; D012969:Sodium Fluoride / Q000032:analysis; D013997:Time Factors; D014100:Toothpastes / Q000032:analysis
chemical_list: D002327:Cariostatic Agents; D010710:Phosphates; D014100:Toothpastes; C012980:fluorophosphate; D012969:Sodium Fluoride; D003404:Creatinine; D005459:Fluorides