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Endocrine Abstracts (2015) 37 EP223 | DOI: 10.1530/endoabs.37.EP223

1DIAsource Immunoassays, Louvain‐la‐Neuve, Belgium; 2Future Diagnostics BV, Wijchen, The Netherlands.


The objective of this project was to develop and characterise a simple immunoassay for the quantification of free 25-hydroxyvitamin D (25OH Vit D). Recent studies suggest that the concentration and genotype of vitamin D binding protein (DBP) are important factors that determine the bioavailability of 25OH Vit D in blood. It has been suggested that measurement of free, non-protein bound 25OH Vit D in serum, may provide more relevant diagnostic information than total 25OH Vit D, for instance in chronic kidney disease, bladder cancer and pancreatic cancer, or in haemodialysis patients. A two-step enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of free 25OH Vit D assay, using a highly specific anti-25OH Vit D monoclonal antibody. The assay was calibrated against a symmetric dialysis method. The calibrator range was 0–35 pg/ml. The LoB was 1.1 pg/ml; the LoD was 1.7 pg/ml. Total assay precision was 5.7% at 6.3 pg/ml, 3.8% at 15.9 pg/ml and 4.8% at 24.8 pg/ml. The assay was recently compared with calculated free 25OH Vit D in clinical populations (J Schwartz J. Clin. Endocrinol. Metab. 2014). An assay was developed that reproducibly determines the level of free 25OH Vit D in serum. The assay can be used as a valuable tool in studies to establish the clinical relevance of free 25OH Vit D.

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