Free 25-hydroxyvitamin D lower in children with renal transplant vs chronic kidney disease

Takeaway

• In children who underwent transplant, vitamin D-binding protein (VDBP) concentrations were significantly higher and free 25-hydroxyvitamin D (25(OH)D) concentrations were lower compared with those with chronic kidney disease (CKD) and those on dialysis, despite comparable total 25(OH)D concentrations.

Why this matters

• Findings question whether the current practice of determining total 25(OH)D concentrations is a most reliable biomarker of vitamin D status and suggest that free-25(OH)D measures may be required in children with CKD, dialysis, and transplant.

Study design

• A post-hoc cross-sectional analysis of 61 children with CKD and who underwent kidney transplant (CKD stages II-III, n=22; dialysis, n=18 and post-transplant, n=21).
• Funding: None.

Key results

• Total 25(OH)D concentrations did not differ between CKD, dialysis and post-transplant groups (P=.09), but free- and bioavailable-25(OH)D (free- and albumin-25(OH)D) were significantly lower in the transplant group (P=.01 for both).
• The transplant group had significantly higher VDBP concentrations vs CKD and dialysis groups (P=.03).
• Total 25(OH)D concentrations were positively associated with measured free-, calculated free- and bioavailable-25(OH)D in all 3 groups.
• In the multivariable regression analysis:
  • Total 25(OH)D was the only predictor of free 25(OH)D concentrations in the dialysis group (β=0.90; R²=0.90; P<.001).
  • In the transplant group, lower total 25(OH)D (β=0.63) and VDBP (β=−0.60; R²=0.80; P<.001 for both) concentrations were independently associated with lower free 25(OH)D concentrations.
• Parathyroid hormone was inversely associated with total-, free- and calculated free-25(OH)D concentrations in the transplant group (P<.001 for all).

Limitations

• Post-hoc analysis.
• Small sample size.