Toward Clarity in Clinical Vitamin D Status Assessment: 25(OH)D Assay Standardization.

Widespread variation in 25-hydroxyvitamin D (25(OH)D) assays continues to compromise efforts to develop clinical and public health guidelines regarding vitamin D status. The Vitamin D Standardization Program helps alleviate this problem. Reference measurement procedures and standard reference materials have been developed to allow current, prospective, and retrospective standardization of 25(OH)D results.

Establishing an Accuracy Basis for the Vitamin D External Quality Assessment Scheme (DEQAS).

Until recently, the Vitamin D External Quality Assessment Scheme (DEQAS) assessed the performance of various assays for the determination of serum total 25-hydroxyvitamin D [25(OH)D] by using a consensus mean based on the all-laboratory trimmed mean (ALTM) of the approximately 1000 participants' results. Since October 2012, the National Institute of Standards and Technology (NIST), as part of the Vitamin D Standardization Program, has participated in DEQAS by analyzing the quarterly serum sample sets using an isotope dilution LC-tandem MS (ID LC-MS/MS) reference measurement procedure to assign an accuracy-based target value for serum total 25(OH)D. NIST has analyzed 90 DEQAS samples (18 exercises × 5 samples/exercise) to assign target values.

Baseline Assessment of 25-Hydroxyvitamin D Assay Performance: A Vitamin D Standardization Program (VDSP) Interlaboratory Comparison Study.

The Vitamin D Standardization Program (VDSP) coordinated an interlaboratory study to assess the comparability of measurements of total 25-hydroxyvitamin D [25(OH)D] in human serum, which is the primary marker of vitamin D status. A set of 50 individual donor samples were analyzed by 15 different laboratories representing national nutrition surveys, assay manufacturers, and clinical and/or research laboratories to provide results for total 25(OH)D using both immunoassays (IAs) and LC tandem MS (MS/MS). The results were evaluated relative to bias compared with the target values assigned based on a combination of measurements at Ghent University (Belgium) and the U.

Baseline Assessment of 25-Hydroxyvitamin D Reference Material and Proficiency Testing/External Quality Assurance Material Commutability: A Vitamin D Standardization Program Study.

The Vitamin D Standardization Program (VDSP) coordinated a study in 2012 to assess the commutability of reference materials and proficiency testing/external quality assurance materials for total 25-hydroxyvitamin D [25(OH)D] in human serum, the primary indicator of vitamin D status. A set of 50 single-donor serum samples as well as 17 reference and proficiency testing/external quality assessment materials were analyzed by participating laboratories that used either immunoassay or LC-MS methods for total 25(OH)D. The commutability test materials included National Institute of Standards and Technology Standard Reference Material 972a Vitamin D Metabolites in Human Serum as well as materials from the College of American Pathologists and the Vitamin D External Quality Assessment Scheme.

General Steps to Standardize the Laboratory Measurement of Serum Total 25-Hydroxyvitamin D.

The Vitamin D Standardization Program (VDSP) has collaborated with numerous groups and agencies to assemble a set of tools, i.e., a reference measurement system, that can be used to establish the traceability of 25-hydroxyvitamin D [25(OH)D] assays to relevant reference measurement procedures and reference materials.

Interlaboratory Comparison for the Determination of 24,25-Dihydroxyvitamin D₃ in Human Serum Using Liquid Chromatography with Tandem Mass Spectrometry.

Six laboratories associated with the Vitamin D Standardization Program (VDSP) participated in an interlaboratory comparison of LC with tandem MS (MS/MS) methods for the determination of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] in human serum. The laboratories analyzed two different serum-based Standard Reference Materials (SRMs) intended for use in the determination of 25-hydroxyvitamin D and 30 samples from the Vitamin D External Quality Assessment Scheme (DEQAS). All laboratory methods for 24,25(OH)2D3 were based on isotope dilution LC-MS/MS; three of the methods used derivatization of the vitamin D metabolites before LC-MS/MS.

Significance of serum 24,25-dihydroxyvitamin D in the assessment of vitamin D status: a double-edged sword?

Background: 24,25-Dihydroxyvitamin D [24,25(OH)2D] in serum may be both a nuisance and nutritionally valuable.

Methods: We investigated the impact of 24,25(OH)2D3 on the performance of commercially available immunoassays for serum total 25-hydroxyvitamin D [25(OH)D] using (a) serum from a nationally representative sample of adults, (b) serum from a spiking experiment, and (c) data from the UK Vitamin D External Quality Assurance Scheme (DEQAS). We also investigated the utility of the serum ratio of 24,25(OH)2D3 to 25(OH)D as an index of inactivation and of response to vitamin D supplementation using randomized controlled trial (RCT) data.

Studies on the analysis of 25-hydroxyvitamin D(3) by isotope-dilution liquid chromatography-tandem mass spectrometry using enzyme-assisted derivatisation.

The total serum concentration of 25-hydroxyvitamins D (25-hydroxyvitamin D3 and 25-hydroxyvitamin D2) is currently used as an indicator of vitamins D status. Vitamins D insufficiency is claimed to be associated with multiple diseases, thus accurate and precise reference methods for the quantification of 25-hydroxyvitamins D are needed. Here we present a novel enzyme-assisted derivatisation method for the analysis of vitamins D metabolites in adult serum utilising 25-[26,26,26,27,27,27-(2)H6]hydroxyvitamin D3 as the internal standard.

Practical guidelines for the supplementation of vitamin D and the treatment of deficits in Central Europe - recommended vitamin D intakes in the general population and groups at risk of vitamin D deficiency.

Introduction: Adequate Vitamin D intake and its concentration in serum are important for bone health and calcium-phosphate metabolism as well as for optimal function of many organs and tissues. Documented trends in lifestyle, nutritional habits and physical activity appear to be associated with moderate or severe Vitamin D deficits resulting in health problems. Most epidemiological studies suggest that Vitamin D deficiency is prevalent among Central European populations.

Accuracy of 25-hydroxyvitamin D assays: confronting the issues.

Measurement of 25-hydroxyvitamin D (25-OHD) is widely used for assessing vitamin D status. There has been a dramatic increase in 25-OHD requests over recent years prompting many laboratories to consider the use of automated immunoassays. To achieve higher throughput, these methods have abandoned the traditional solvent extraction of samples and are therefore more prone to non-specific interference.

Use of a common standard improves the performance of liquid chromatography-tandem mass spectrometry methods for serum 25-hydroxyvitamin-D.

Background: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is becoming increasingly popular for measuring 25-hydroxyvitamin-D (25-OH-D). Results submitted to the International Quality Assessment Scheme (DEQAS) have shown poor interlaboratory agreement. We investigated whether the use of a common standard would reduce interlaboratory imprecision.

Contemporary diagnosis and treatment of vitamin D-related disorders.

Plasma 25(OH)D has emerged as a valuable biomarker for the many varied health-related effects of vitamin D in the clinic mainly because of the recognition of the importance of the enzyme, CYP27B1, or the 25(OH)D-alpha-hydroxylase in the extrarenal, target cell production of calcitriol. This review briefly assesses current methodology for plasma 25(OH)D assay focusing mainly on currrent controversies surrounding the definition of the normal range and performance characteristics of the assay, separate measurement of both 25(OH)D(2) and 25(OH)D(3), and quality assurance tesing of laboratories offering the test. Clinicians have two main types of 25(OH)D assay based on either high-performance liquid chromatography with UV or mass detection or higher throughput kits based on protein (competitive protein binding assay or radioimmunoassay) binding.