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Abstract: PO0571

The Vitamin D Metabolite Ratio May Serve as an Important Biomarker of Vitamin D Status in Patients Undergoing Therapeutic Plasma Exchange

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical

Authors

  • Dugar, Anushree, University of California San Diego School of Medicine, La Jolla, California, United States
  • Hoofnagle, Andrew N., University of Washington, Seattle, Washington, United States
  • Sanchez, Amber P., University of California San Diego Department of Medicine, La Jolla, California, United States
  • Ward, David M., University of California San Diego Department of Medicine, La Jolla, California, United States
  • Cheng, Jonathan, University of California San Diego Department of Medicine, La Jolla, California, United States
  • Ix, Joachim H., University of California San Diego Department of Medicine, La Jolla, California, United States
  • Ginsberg, Charles, University of California San Diego Department of Medicine, La Jolla, California, United States
Background

Recent studies suggest that 25-hydroxyvitamin D [25(OH)D] may be a poor marker of vitamin D status due to variability in levels of vitamin D binding protein (VDBP). The vitamin D metabolite ratio (VMR) is the ratio of 24,25(OH)2D3: 25(OH)D3 and is thought to be independent of variability in VDBP. Therapeutic plasma exchange (TPE) is a procedure that removes VDBP and thus may lower vitamin D metabolites. The effects of TPE on free vitamin D concentrations and the VMR remains unknown.

Methods

We measured total 25(OH)D, 1,25(OH)2D, 24,25(OH)2D3, and VDBP using Liquid chromatography–mass spectrometry, and free 25(OH)D using a DIAsource ELISA assay in 45 patients undergoing TPE. Levels were measured before and after a single TPE. We used the paired t-test to assess changes in 25(OH)D, 1,25(OH)2D, 24,25(OH)2D3, free 25(OH)D, VDBP and VMR across TPE.

Results

Study participants had a mean age of 55 ± 16 years; 67% were female; 76% were white; one of 45 had CKD. TPE caused a significant decrease in total 25(OH)D, 1,25(OH)2D, 24,25(OH)2D3, and free 25(OH)D. There was no change in the VMR from before to after TPE (Table 1).

Conclusion

Changes in VDBP concentration across TPE parallel changes in 25(OH)D, 1,25(OH)2D, and 24,25(OH)2D3 suggesting that levels of these metabolites may be markers of VDBP levels. The lack of change in VMR across TPE despite a significant change in VDBP suggests that VMR is independent of VDBP levels. The VMR may therefore serve as an important biomarker of vitamin D status in populations with a large spectrum of VDBP concentrations.

Changes in Vitamin D Metabolites, VDBP, and VMR from Before to After a Single TPE Procedure (N=45)
 25(OH)DFree 25(OH)D24,25(OH)2D31,25(OH)2DVDBPVMR
% change after TPE (95% CI)-66% (-70%,-62%)-31% (-38%,-24%)-66% (-72%,-60%)-68% (-72%,-64%)-65% (-68%,-63%)6% (-2%, 14%)
p-value<.001<.001<.001<.001<.0010.160