An evaluation of total 25-hydroxyvitamin D assay standardization: Where are we today?. Issue 190 (June 2019)

• Record Type: Journal Article
• Authors: Bjerg, Lise Nørkjær; Halgreen, Jens Romlund; Hansen, Svend Høime; Morris, Howard A.; Jørgensen, Niklas Rye
• Is Part Of: Journal of steroid biochemistry and molecular biology. Issue 190(2019)
• Page Start: 224
• Page End: 233
• Publication Date: 2019-06
• Subjects: Vitamin D standardization program -- 25-Hydroxyvitamin D; Steroid hormones -- Periodicals; Biochemistry -- Periodicals; Hormones -- Periodicals; Molecular Biology -- Periodicals; Hormones stéroïdes -- Périodiques; Steroid hormones; Periodicals; 572.579
• DOI: 10.1016/j.jsbmb.2019.03.015
• Languages: English
• ISSNs: 0960-0760

Abstract

Highlights: Only few 25(OH) D assays comply with requirements in the Vitamin D Standardization Program. 25(OH) assays vary greatly in the categorization of patients in vitamin D deficiency/sufficiency. Standardization has been obtained in some 25(OH)D immunoassays. Abstract: Background: Serum total 25-hydroxyvitamin D is a measure of the total circulating 25-hydroxyvitamin D concentration and is the primary measurement for estimating vitamin D status. A number of automated immunoassays are commercially available, and in an attempt to standardize the assays the Vitamin D Standardization Program (VDSP) was established in 2010. Therefore, the aim of the current project is to evaluate the status of the standardization of routinely used 25-hydroxyvitamin D assays. Methods: 200 patient serum samples were measured in Spring 2017 on seven different assays for 25-hydroxyvitamin D. Samples were measured in duplicate for the evaluation of precision. A certified standard reference material (SRM972a) from The National Institute of Standardization and Technology (NIST) was measured to evaluate the accuracy of the assays. Finally, the agreement of the assays of clinically categorizing patients into vitamin D deficiency, inadequacy or adequacy was evaluated. Results: All seven assays achieved precision below the VDSP requirement of CV < 10%. However, only two of the assays achieved an accuracy bias <5% when measuring the SRM972a. When comparing methods using Deming regression, substantial proportional and/or systematic bias was found between many of the assays. Finally, when evaluating the ability of the assays to categorize patients into "vitamin D deficiency" (25-hydroxyvitamin D concentration < 30 nmol/L (<12 ng/mL)), "vitamin D inadequacy" (30–50 nmol/L (12–20 ng/mL)), "vitamin D adequacy" (50–250 nmol/L (20–100 ng/mL)) and "risk of toxicity" (>250 nmol/L (>100 ng/mL)), clinically relevant differences between assays were detected. Especially in the deficiency group, major discrepancies were found as the percentage of patients ranged from 1.5%–14.3% between the assays.. Conclusions: In conclusion, some of the commercially available assays have been standardized with performance as required by the VDSP. However, several of the assays do still not comply with the VDSP requirements even eight years after the program was started. This may have clinical consequences for patients, and manufacturers are therefore encouraged to continue their work on standardizing serum 25-hydroxyvitamin D assays.