Some previous studies indicate extra fluoride retention in human bones caused by severe renal insufficiency. Plasma and serum fluoride concentrations may also be elevated in a fluoridated community. The results from low-fluoride areas are less consistent. The first aim of the present study was thus to test the relation between ionic serum fluoride concentration and renal function in patients with kidney disease in an area where there is only 0.1-0.2 ppm fluoride in the drinking water.
Earlier calculations indicate that a creatinine clearance lower than 16 ml/min induces extra fluoride accumulation. The threshold may be even lower. The second aim was therefore to relate daily fluoride excretion of each individual to his/her renal function capacity to find out which level of renal impairment causes fluoride accumulation to begin.
Thirdly, the earlier series concerning fluoride retention in renal patients were not properly selected. The present series was divided into two groups according to the place of residence of the patients to test the effeet of the place of residence on the results.
The results showed a good linear inverse correlation between individual serum fluoride concentrations and log serum creatinine levels for both city residents and non-resident renal patients. If the serum creatinine levels had not been converted to their logarithms, the regression line would have been curved, as in the previous, less controlled study.
Both groups of patients with renal disease had significantly elevated serum fluoride concentrations and excreted distinctly less fluoride than their controls.
The correlation between fluoride excretion in 24 hours and the serum creatinine concentrations indicates that renal insufficiency can quite easily give rise to fluoride retention. When the serum creatinine concentration exceeds 114 umol/I, the fluoride excretion /24 hours becomes inhibited, especially in city residents. Thus the loss of even half of the renal excretory capacity may result in slight fluoride retention.
Finally, the comparison of the results between the city residents and non-residents demonstrates very similar trends in both groups. The findings are very similar to those obtained earlier with the mixed series. It is therefore concluded that the only possible error caused by the material in the previous results is in the mean fluoride concentrations, which might have been slightly lower if the patients had been more carefully selected.