Measurement of total and diffusible serum fluoride

This article describes a technique far the measurement of total and diffusi ble F content of serum, at clinical significant concentrations of F (1-10 m u M). The proposed procedure avoids the interference of unknown serum compo nents with the ion-specific electrode. Sample F is concentrated fivefold th rough distillation of hydrofluoric acid (Taves' method). Ionic fluoride is presented to the electrode in a simple solution at concentrations within th e linear response of the electrode. Average recoveries of F from serum or i ts ultrafiltrate were 96 +/- 7% (21%) and 97 +/- 12% (53%) (mean +/- SEM [C V]), respectively. With four replicates of each sample, the technique produ ce within-run standard deviations of 0.6 mu M and 2.2 mu M at 1 and 10 mu M F, respectively. Total precision assessment gave standard deviations of 0. 6 mu M and 2.6 mu M at 1 and 10 mu M F, respectively. The fasting serum F l evels of normal climacteric women, 45 to 65 years, showed an asymmetric dis tribution. The data obtained started at the detection limit of the techniqu e (0.1 mM). The 75 percentile was 1.85 mu M for total and 0.5 mu M for diff usible F. In patients (n = 25) treated with NaF (30 mg F/day) the fasting l evels of total serum F (4.5 +/- 1.7 mu M) did not differ from those of diff usible F (4.2 +/- 1.5 mu M). In patients (n = 50) treated with sodium monof luorophosphate (15 mg F/day) the fasting levels of total and diffusible ser um F were 6.5 +/- 1.7 mu M and 0.5 +/- 0.03 mu M, respectively. In conclusi on, this paper establishes the presence of two fractions of serum fluorine: diffusible and nondiffusible (or protein bound) and describes a technique for their clinical estimation. In untreated subjects and in patients receiv ing NaF, the former fraction contains ionic fluoride. In patients treated w ith MFP, diffusible serum fluorine is composed by ionic fluoride and low mo lecular weight, peptide-bound, acid-labile fluorine. J. Clin. Lab. Anal. 13 :151-157, 1999. (C) 1999 Wiley-Liss, Inc.