= Emerging. More than 5 years before clinical availability. (19.79%)
= Expected to be clinically available in 1 to 4 years. (37.97%)
= Clinically available now. (42.25%)
MSACL 2022 : Kushnir

MSACL 2022 Abstract

Self-Classified Topic Area(s): Cases in Clinical MS > none > none

Podium Presentation in De Anza 1 on Thursday at 15:35 (Chair: Julie Ray / Amol Bajaj)

Free 25-hydroxy Vitamin D Measured by LC-MS/MS in Healthy Adults and Individuals with Kidney Disease

Mark M. Kushnir1,2, Cora M. Best3,4, Andrew N. Hoofnagle3,4,5
1ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT; 2Department of Pathology, University of Utah, Salt Lake City, UT; 3Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA; 4Kidney Research Institute, University of Washington, Seattle, WA; 5Department of Medicine, University of Washington, Seattle, WA

Mark Kushnir (Presenter)
ARUP Institute for Clinical & Experimental Pathology

Presenter Bio: Mark Kushnir is Scientific Director, Mass Spectrometry R&D at ARUP Institute for Clinical and Experimental Pathology and Adjunct Assistant Professor at the Department of Pathology, University of Utah School of Medicine. Mark received PhD in Analytical Chemistry from Uppsala University (Uppsala, Sweden); his main areas of interest include development, application and clinical evaluation of novel mass spectrometry based clinical diagnostic methods for small molecule, protein and peptide biomarkers. He is author/coauthor of over 100 scientific peer reviewed publications.


Serum 25-hydroxy vitamin D (25OHD) is widely used as a biochemical marker of vitamin D status. Most 25OHD circulating in blood is tightly bound to vitamin D binding protein, a smaller fraction is weakly bound to albumin, and a very small fraction (<0.1%) is present in a free form. It has been demonstrated that most cells in the human body respond to free rather than bound 25OHD and as a result, concentrations of free 25OHD (F25OHD) are likely more relevant than total 25OHD (T25OHD) for the assessment of vitamin D status. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the measurement of F25OHD2 and F25OHD3 and used the method in a study of the effect of percent F25OHD on 25OHD clearance in individuals with and without kidney function impairment.

Sample preparation in the method was performed as follows: F25OHD2/ F25OHD3 were separated from the protein bound fraction using size exclusion-based separation; the analytes and the corresponding internal standards were derivatized using Ampliflex diene reagent (Sciex), and the samples were analyzed by LC-MS/MS. The instrumental analysis utilized two-dimensional chromatographic separation with data acquisition performed on a Triple QuadTM 6500 (Sciex). The lower limit of quantification of the assay for F25OHD2 and F25OHD3 was 0.005 ng/mL, and the total imprecision was <18%. Reasonably good correlation (r=0.873, n=62) was observed with a commercial ELISA (DIAsource), while concentrations measured by the ELISA were significantly lower than by the LC-MS/MS method. In the study on the effect of percent F25OHD on 25OHD clearance, we determined the serum T25OHD concentrations using LC-MS/MS; and F25OHD concentrations using a) LC-MS/MS, b) commercial ELISA (DIAsource), and c) calculation-based method, in samples of healthy adults (n=42), adults with chronic kidney disease (n=24) and kidney failure (n=19). We assessed agreement among the 3 methods and the association of F25OHD concentrations with the kidney function.

We observed reasonably good correlation between the LC-MS/MS method and the commercial ELISA (r=0.61, n=42) in samples of healthy adults, while the concentrations by the ELISA were on average 10 times lower as compared to the LC-MS/MS method. Significant negative biases were observed in the ELISA measured F25OHD concentrations among participants with kidney failure, as compared to the LC-MS/MS, suggesting potential sample matrix interference with the ELISA measurements in these samples. In samples of healthy adults, we observed reasonably good correlation between the measured by LC-MS/MS and the calculated concentrations of F25OHD (r=0.83, n=42). The percent F25OHD determined by the calculation-based method was weakly associated with 25OHD clearance, while this association was absent when percent F25OHD was determined using LC-MS/MS-measured F25OHD and T25OHD concentrations.

In conclusion, sensitivity and specificity of the LC-MS/MS method for F25OHD were adequate for measurement of endogenous F25OHD concentrations in samples from healthy individuals and patients with kidney disease. Our data suggest that percent F25OHD is not strongly associated with 25OHD clearance and that the percent F25OHD is not altered in patients with kidney failure as compared to individuals with normal kidney function. We determined that, when F25OHD concentrations were measured by the commercial ELISA, the apparent decrease in percent F25OHD in association with kidney failure was an artifact caused by interference in the ELISA.

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