Free 25-hydroxyvitamin-D concentrations are lower in children with renal transplant compared with chronic kidney disease

Evgenia Preka, Mandy Wan, Karen L Price, David A Long, Helen Aitkenhead, Rukshana Shroff

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

BACKGROUND: Total serum 25-hydroxyvitamin D [25(OH)D] is considered the best marker of vitamin D status and used routinely in clinical practice. However, 25(OH)D is predominantly bound to vitamin D-binding protein (VDBP), and it has been reported that the free-25(OH)D and 25(OH)D loosely bound to albumin fraction correlates better with clinical outcomes.

METHODS: We assessed total-25(OH)D, measured free-25(OH)D, and calculated free-25(OH)D and their relationship with VDBP and biomarkers of mineral metabolism in 61 children (22 CKD 2-3, 18 dialysis, and 21 post-transplant).

RESULTS: Total-25(OH)D concentrations were comparable across the three groups (p = 0.09), but free- and bioavailable-25(OH)D (free- and albumin-25(OH)D) were significantly lower in the transplant group (both: p = 0.01). Compared to CKD and dialysis patients, the transplant group had significantly higher VDBP concentrations (p = 0.03). In all three groups, total-25(OH)D concentrations were positively associated with measured free-, calculated free-, and bioavailable-25(OH)D. Multivariable regression analysis showed that total-25(OH)D was the only predictor of measured free-25(OH)D concentrations in the dialysis group (β = 0.9; R2 = 90%). In the transplant group, measured free-25(OH)D concentrations were predicted by both total-25(OH)D and VDBP concentrations (β = 0.6, - 0.6, respectively; R2 = 80%). Correlations between parathyroid hormone with total-25(OH)D and measured and calculated free-25(OH)D were only observed in the transplant group (all: p < 0.001).

CONCLUSIONS: In transplanted patients, VDBP concentrations were significantly higher compared to CKD and dialysis patients, and consequently, free-25(OH)D concentrations were lower, despite a comparable total-25(OH)D concentration. We suggest that free-25(OH)D measures may be required in children with CKD, dialysis, and transplant, with further research required to understand its association with markers of mineral metabolism.

Original languageEnglish
Pages (from-to)1069-1079
Number of pages11
JournalPediatric nephrology (Berlin, Germany)
Volume35
Issue number6
DOIs
Publication statusPublished - Jun 2020

Keywords

  • Adolescent
  • Biomarkers/blood
  • Child
  • Child, Preschool
  • Cross-Sectional Studies
  • Female
  • Humans
  • Kidney Transplantation
  • Male
  • Renal Dialysis
  • Renal Insufficiency, Chronic/blood
  • Vitamin D/analogs & derivatives
  • Vitamin D Deficiency/blood
  • Vitamin D-Binding Protein/blood

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