Abstract
Vitamin D status in different populations relies on accurate measurement of total serum 25-hydroxyvitamin D [25(OH)D] concentrations [i.e., 25(OH)D3 and 25(OH)D2]. This study evaluated agreement between the ADVIA Centaur Vitamin D Total assay for 25(OH)D testing (traceable to the NIST-Ghent reference method procedure) and a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for various populations with different levels of vitamin D binding protein (DBP). Total serum 25(OH)D concentrations were measured for 36 pregnant women, 40 hemodialysis patients, and 30 samples (DBP-spiked or not) from healthy subjects. ELISA measured DBP levels. The mean serum DBP concentrations were higher for pregnancy (415 μg/mL) and lower for hemodialysis subjects (198 μg/mL) than for healthy subjects and were highest for spiked serum (545 μg/mL). The average bias between the ADVIA Centaur assay and the LC-MS/MS method was −1.4% (healthy), −6.1% (pregnancy), and 4.4% (hemodialysis). The slightly greater bias for samples from some pregnancy and hemodialysis subjects with serum DBP levels outside of the normal healthy range fell within a clinically acceptable range—reflected by analysis of their low-range (≤136 μg/mL), medium-range (137–559 μg/mL), and high-range (≥560 μg/mL) DBP groups. Thus, the ADVIA Centaur Vitamin D Total assay demonstrates acceptable performance compared with an LC-MS/MS method for populations containing different amounts of DBP.
Highlights
Increasing awareness of the important role of vitamin D for bone and other diseases has led to increased 25hydroxyvitamin D [25(OH)D] testing (D represents D3 and D2 forms)
Radioimmunoassays, high performance liquid chromatography (HPLC), and mass spectrometry methods for 25(OH)D testing are subject to variability issues that can arise from a variety of sources, such as differential detection of the D3 and D2 forms, interference by detection polyclonal antibodies, and nonspecific detection of other vitamin D metabolites such as the 3-epimer form of 25(OH)D [3epi-25(OH)D] and 24,25(OH)2D3
D binding protein (DBP) binds vitamin D3 along with other metabolites and vitamin D2, whose similar structures may be easier to release from DBP and difficult to differentiate; DBP has a higher affinity for vitamin D3 than other metabolites and vitamin D2 [8]; and generating specific antibodies against small antigenic molecules, such as 25(OH)D, is difficult, but it is mandatory because the Vitamin D Standardization Program (VDSP) states that 25(OH)D assays should measure
Summary
Increasing awareness of the important role of vitamin D for bone and other diseases has led to increased 25hydroxyvitamin D [25(OH)D] testing (D represents D3 and D2 forms). Radioimmunoassays, high performance liquid chromatography (HPLC), and mass spectrometry methods for 25(OH)D testing are subject to variability issues that can arise from a variety of sources, such as differential detection of the D3 and D2 forms, interference by detection polyclonal antibodies, and nonspecific detection of other vitamin D metabolites such as the 3-epimer form of 25(OH)D [3epi-25(OH)D] and 24,25(OH)2D3. Incomplete release of 25(OH)D from the vitamin D binding protein (DBP) has been identified as a potential source of variability for both manual and automated immunoassays [6]. DBP binds vitamin D3 along with other metabolites and vitamin D2, whose similar structures may be easier to release from DBP and difficult to differentiate; DBP has a higher affinity for vitamin D3 than other metabolites and vitamin D2 [8]; and generating specific antibodies against small antigenic molecules, such as 25(OH)D, is difficult, but it is mandatory because the Vitamin D Standardization Program (VDSP) states that 25(OH)D assays should measure
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