Effects of Age and Diseases on Human Serum 25-Hydroxycholecalcif erol Determined by Competitive Protein-Binding Assay

Abstract

Competitive protein-binding assay of 25-OH-D was developed by the use of specific vitamin D-binding proteins from vitamin D-deficient rat serum. Ether extract of serum sample which was dried and dissolved in ethanol, or standard solution of 25-OH-D3, was incubated with ³H-25-OH-D₃ and vitamin D-binding protein for 2 hours at 4°C. Free and bound ³H-25-OH-D₃ were separated through dextran-coated charcoal. The sensitivity of the assay system was 0.22 ng/tube. Percent cross reaction in the assay was 2.18% in vitamin D₃, 0.70% in 1, 25-(OH) ₂-D₃, less than 0.28% in la-OH-D₃, and less than 0.06% in dihydrotachysterol, cholesterol and cortisol.
Human serum 25-OH-D is 28.9±2.9 ng/ml in 19 normal subjects. Serum 25-OH-D in the old-age group (50-70 years of age) was significantly decreased, compared with that in the young-age group (20-40 years of age). Serum 25-OH-D was significantly decreased in gastrectomized and osteoporotic patients as well as in the patients with liver cirrhosis, in comparison with their age-controls.