DOES VITAMIN D BINDING PROTEIN INTERFERE IN THE SIEMENS ADVIA CENTAUR VITAMIN D TOTAL ASSAY?

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 257-280-Disorders of Vitamin D Metabolism & Action
Basic/Translational
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-276
James Freeman*1, Paul Sibley2 and Kim Wilson3
1Siemens Healthcare Diagnostics, Tarrytown, NY, 2Siemens Healthcare Diagnostics, Gwynedd, United Kingdom, 3Siemens Healthcare Diagnostics, Los Angeles, CA
Introduction: Following a literature report on the influence of Vitamin D Binding Protein (VDBP) in routine 25-hydroxyvitamin D (25(OH)vitamin D) assays (Heijboer et al, Clin Chem 58; 345-349, 2012), the effect of both exogenous and endogenous VDBP on the Siemens ADVIA Centaur®  Vitamin D Total assay was evaluated. Determination of vitamin D concentrations in automated immunoassays require extraction of 25(OH)vitamin D from the VDBP, which is bound at high affinity (Ka = 5x10-8M) and is thought to be present in approximately 5% of the available VDBP in the circulation.

Objectives: The objectives of the study were to assess the impact of exogenously added VDBP to pools of normal serum and also to evaluate several clinical samples with varying concentrations of endogenous VDBP, which were also used for exogenous application using both the Siemens ADVIA Centaur Vitamin D Total assay and LC-MS/MS.

Patients and Methods: The study design for the VDBP exogenous work involved five serum pools containing only 25(OH)vitamin D3, prepared using LC-MS/MS values: pool 1 (24 ng/mL), pool 2 (32 ng/mL), pool 3 (51 ng/mL), pool 4 (41 ng/mL) and pool 5 (75 ng/mL). A > 95% pure human native VDBP was purchased and, following endogenous measurement of VDBP in the pools, the native VDBP was spiked into each pool at various levels. VDBP was reanalyzed in each pool using a microplate enzyme immunoassay method (R&D Systems). Vitamin D concentration was determined in each pool and subset using the ADVIA Centaur Vitamin D Total assay and LC-MS/MS. Clinical samples from pregnancy patients (3rd trimester) and chronic kidney disease patients, allowing a wide range of VDBP concentrations, were also evaluated. 

Results: In the five serum pools the levels of endogenous DBP ranged from 260.7 µg/mL to 519.0 µg/mL (average 347.7 µg/mL), which is consistent with other studies. The average bias for all normal samples (endogenous DBP and spiked DBP) for the ADVIA Centaur assay was 0.0%. The average bias for all pregnancy samples (endogenous DBP and spiked DBP) for the ADVIA Centaur assay was -6.0%. The average bias for all renal dialysis samples (endogenous DBP and spiked DBP) for the ADVIA Centaur assay was 6%. This demonstrates there was not a significant bias observed for the ADVIA Centaur to LC-MS/MS due to increasing levels of spiked DBP in normal serum pools or patients with clinical conditions such as pregnancy or chronic kidney disease.

Conclusion: The impact of VDBP concentration at levels much higher than would be found in native patient samples and patients with clinical conditions such as pregnancy or chronic kidney disease was negligible, and this could also be evaluated by the bias to LC-MS/MS, which was within assay limits. This work indicates that the concentration of VDBP has minimal impact on the concentration of 25(OH) vitamin D measured by the ADVIA Centaur Vitamin D Total assay.

Disclosure: JF: Employee, Siemens Healthcare Diagnostics, Employee, Siemens Healthcare Diagnostics. PS: Employee, Siemens Healthcare Diagnostics. KW: Employee, Siemens Healthcare Diagnostics.

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Siemens Healthcare Diagnostics