Competitive Protein-Binding Assay for 25-Hydroxycholecalciferol

Abstract

911 Comment Increases in osteoid volume with sodium fluoride, calcium, and vitamin D treatment are well documented. Small decreases in mineralisation rate have also been reported.2 But osteomalacia in the presence of high plasma 25-OHD concentrations has not been described in patients treated with this regimen. The plasma 1,25-(OH)2D3 concentration in our patient was just below the lower limit of normal, but the total plasma 1,25-(OH)2D (1,25-(OH)2D2-+1,25-(OH)2D3) concentration was probably normal since she was taking vitamin D2 and the radioimmunoassay did not measure plasma 1,25-(OH)2D2. The mechanisms by which fluoride may produce osteomalacia despite high plasma 25-OHD concentrations require further investigation. Possibilities include fluoride-induced end-organ resistance in bone to active vitamin D metabolites or an effect of fluoride on processes of bone mineralisation that are unaffected by vitamin D metabolites. Alternatively, fluoride might affect the metabolism of 25-OHD to other metabolites. Although lack of calcium supplements was probably unimportant in our patient, since the plasma calcium concentration remained above 2 40 mmol,l throughout treatment and dietary calcium intake was adequate, we cannot exclude it as a factor in the development of osteomalacia. Our results indicate that vitamin D in doses that produce high plasma 25-OHD concentrations does not protect against fluoride-induced mineralisation defects and that patients treated with this regimen require careful supervision. Trans-iliac biopsy provides a sensitive method for diagnosing generalised bone disease such as osteomalacia and may be necessary to detect its development when, as in our patient, plasma biochemical changes are not diagnostic. We thank J Sainsbury Ltd and the Special Trustees, St Thomas's Hospital, for generous financial support, and Dr T L Clemens, the Middlesex Hospital, London, WI, for 1,25-(OH)2D3 assays. Jowsey J, Riggs BL, Kelly PJ, Hoffman DL. Effect of combined therapy with sodium fluoride, vitamin D and calcium in osteoporosis. AmJ Med 1972 ;53 :43-9. 2 Meunier PJ, Bressot C, Vignon E, et al. Radiological and histological evolution of post-menopausal osteoporosis treated with sodium fluoride, vitamin D, and calcium. Preliminary results. In: Courvoisier B, Donath A, Baud CA, eds. Fluoride and bone. Berne: Hans Huber, 1978:263-76. 3Cass RM, Croft JD, Perkins P, Nye W, Waterhouse C, Terry R. New bone formation in osteoporosis following treatment with sodium fluoride.

Immunological and immunoassay studies of the binding protein for vitamin D and its metabolites in human serum.

“…The assay was generally similar to competitive protein-binding assays reported by others (12)(13)(14)(15)(16), except that the reported assays have used other sources of binding proteins, including kidney cytosol from rachitic rats (12), serum from normal (13) and rachitic (14, 15) rats, and plasma from an osteomalacic man (16). Serum was extracted by shaking the 0.5-ml sample with 2 ml of ethanol and 3 ml of hexane; phase separation was achieved by adding 2 ml of water and centrifuging.…”

Relation between calcium absorption and serum calcitriol in normal men: evidence for age-related intestinal resistance to calcitriol

“…We have taken a value of a greater than 0.56 fx/h to be normal (Need et al, 1987). Serum was analysed for calcitriol by HPLC followed by radioimmunoassay (Taylor et al, 1980) (normal range 50-160 pmol/l) and 25 hydroxyvitamin D (25(OH)D) by a protein binding assay (Edelstein et al, 1974). A 24-h urine collection was provided by each subject (collected within the week prior to, or following, their hospital visit) and analysed for calcium, phosphate, sodium and creatinine.…”

25-Hydroxyvitamin D and Total Calcium: Extraordinarily Low Plasma Concentrations in Saudi Mothers and Their Neonates

“…Total serum calcium was measured by colorimetric methods (Boehringer Mannheim GmbH, Diagnostica). Serum 25-0HD was quantitated by competitive proteinbinding assay using rachitic rat serum as described by Edelstein et al (7). The percentage of the overall recovery of added 3H_ labeled 25-hydroxyvitamin D 3 (Amersham International, U. K.) was 79.8 ± 3.90.…”