Determination of 25-hydroxyvitamin D3 in human serum by fluorescence labelling and high-performance liquid chromatography

Assessing vitamin D metabolism - four decades of experience

One hundred years ago, the role of vitamin D for bone mineralization and the prevention of rickets was discovered. Vitamin D comprises a group of over 50 metabolites with multiple functions that go far beyond calcium homeostasis and bone mineralization. Approximately 50 years ago, first methods for the measurement of 25-hydroxyvitamin D (25(OH)D) in human blood were developed. Over the years, different analytical principals were employed including competitive protein binding assays, high-performance liquid chromatography, various immunoassay and mass spectrometric formats. Until the recent standardization of serum 25(OH)D measurement, agreement between methods was unsatisfactory. Since then, comparability has improved, but substantial variability between methods remains. With the advent of liquid chromatography tandem mass spectrometry (LC-MS/MS), the accurate determination of 25(OH)D and other metabolites, such as 24,25(OH)2D, becomes increasingly accessible for clinical laboratories. Easy access to 25(OH)D testing has triggered extensive clinical research showing that large parts of the population are vitamin D deficient. The variable response of vitamin D deficient individuals to supplementation indicates that assessing patients' vitamin D stores by measuring 25(OH)D provides limited insight into the metabolic situation. Meanwhile, first evidence has emerged suggesting that the simultaneous measurement of 25(OH)D, 24,25(OH)2D and other metabolites allows a dynamic evaluation of patients' vitamin D status on metabolic principals. This may help to identify patients with functional vitamin D deficiency from those without. It can be expected that research into the assessment vitamin D status will continue for another 50 years and that this will help rationalizing our approach in clinical practice.

Determination of vitamin D3 metabolites: state-of-the-art and trends

The steps involved in the methods for the determination of vitamin D3 metabolites (namely, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3) mainly in clinical samples are critically reviewed. Sample pretreatment (e.g. deproteinization, saponification, liquid liquid and liquid solid extraction, etc.) as a function of both type of sample and detection system, quantitation based on protein saturation and liquid as well as gas chromatography are discussed. The chemical principles on which the methods are based and the derivatization procedures, which facilitate separation and/or detection, are also commented upon. Finally, the future prospects of the research on methods for the determination of these metabolites are outlined.

Determination of 25-hydroxyvitamin D3 in human plasma using a non-radioactive tetranorvitamin D analogue as an internal standard

A convenient non-radioactive method for assaying plasma 25-hydroxyvitamin D3 is described. The method uses 22-hydroxytetranorvitamin D3 as an internal standard and includes two-step liquid- and solid-phase extractions and quantification by normal-phase HPLC. The intra- and inter-assay coefficients of variation were 2.2% and 2.4%, respectively, and the analytical recovery of 25-hydroxyvitamin D3 added to plasma was quantitative. Assay linearity was obtained in the range 0.5-4.0 ml of plasma. When compared with the method employing a radioactive 25-hydroxyvitamin D3 tracer, the correlation coefficient was 0.990 (slope 0.999 and intercept 1.19 ng/ml).