Hydroxyvitamin D assays: An historical perspective from DEQAS

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Analytical Chemistry

Background:

• Demand for 25-hydroxyvitamin D (25-OHD) assays has surged.
• The Vitamin D External Quality Assessment Scheme (DEQAS) has monitored assay performance since 1989.
• Early assays showed high inter-laboratory variability.

Purpose of the Study:

• To review the historical development of 25-OHD assay technology.
• To analyze DEQAS data to illustrate assay improvements over 27 years.
• To highlight challenges in obtaining reliable 25-OHD measurements.

Main Methods:

• Analysis of DEQAS distribution data from 1989 to 2017.
• Tracking the evolution of 25-OHD assay methodologies (e.g., RIA, automated non-isotopic, LC-MS/MS).
• Assessment of assay accuracy against reference measurement procedures (RMPs) since DEQAS became accuracy-based in 2013.

Main Results:

• Inter-laboratory CVs for 25-OHD assays decreased from over 50% in 1989 to approximately 10% in 2017.
• Significant milestones include the development of iodinated tracers and the adoption of LC-MS/MS.
• The Vitamin D Standardization Program (VDSP) promotes standardization through RMPs from NIST, University of Ghent, and CDC.

Conclusions:

• Assay technology for 25-OHD has advanced significantly, leading to improved accuracy and reduced variability.
• Continued efforts in standardization are crucial for reliable 25-OHD measurements.
• DEQAS data provides valuable insights into the historical performance and evolution of 25-OHD testing.