Vitamin D test results still vary by about 9 percent – March 2012

Current 25-hydroxyvitamin D assays: Do they pass the test?

Clin Chim Acta. 2012 Mar 20.
Ong L, Saw S, Sahabdeen NB, Tey KT, Ho CS, Sethi SK.
Department of Laboratory Medicine, National University Hospital, Singapore.

BACKGROUND:
Vitamin D testing is becoming increasingly important with recent research demonstrating a correlation between vitamin D insufficiency and metabolic diseases, immunodeficiencies and other diseases. However, existing 25-hydroxyvitamin D (25OHD) assays lack comparability to the candidate reference method, causing difficulties in diagnosis and monitoring of vitamin D deficiency.

METHODS:
We looked at the accuracy of 3 automated assays (Roche Diagnostics Elecsys® Total 25OHD assay, Abbott Architect® Total vitamin D assay, Advia Centaur® vitamin D Total assay) and Diasorin® Radioimmunoassay (RIA) compared to a routine laboratory Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

RESULTS:
The correlation based on Passing Bablok regression was good with the slopes between 0.95 and 1.31 and the intercepts between -3.24 and 3.68. However, a significant positive bias was observed using the Abbott Architect and the Diasorin RIA.

Using published analytical goals of coefficient of variation (CV) <10% and bias <5%, most methods did not meet these criteria.

Using measurement of uncertainty of 9%, most methods were able to meet criteria using quality control materials but not patient samples.

CONCLUSION:
Inadequacies of these assay performances are contributed by differences in method of extraction of vitamin D from vitamin D binding protein, cross-reactivities to 25OHD(2), 25OHD(3) and other vitamin D metabolites, matrix interferences and a lack of standardization.

Copyright © 2012. Published by Elsevier B.V.

PMID: 22465235

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See also VitaminDWiki

• Percent who are Vitamin D Deficient: 6, 9, or 22 – depends on testing system – Oct 2014
• All items in category Test for D 160 items
• Different measurements from 6 vitamin D testing systems – Mar 2012 which has the following