Vitamin D Binding Protein (VDBP) significantly decreases in case of kidney disease. This decrease leads to an increase in the free 25OH Vitamin D concentration, at constant total 25OH Vitamin D levels. Therefore several research groups have studied the importance of free 25OH Vitamin D during kidney disease.

• BANERJEE S. (2020)

Free vitamin D levels in steroid-sensitive nephrotic syndrome and healthy controls

Pediatr Nephrol; 35(3):447-454.
https://www.ncbi.nlm.nih.gov/pubmed/31845055

• PREKA E. (2020)

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

Pediatr Nephrol. 2020 Jun;35(6):1069-1079
https://www.ncbi.nlm.nih.gov/pubmed/31970483

• REBHOLZ C. (2015)

Biomarkers of Vitamin D Status and Risk of ESRD.

Am J Kidney Dis. 2015 Oct 13. pii: S0272-6386(15)01161-0.

https://www.ncbi.nlm.nih.gov/pubmed/26475393

• VIVEKANAND J. (2015)

Bioavailable vitamin D levels are reduced and correlate with bone mineral density and markers of mineral metabolism in adults with nephrotic syndrome.

Nephrology (Carlton) Oct 1.

https://www.ncbi.nlm.nih.gov/pubmed/26428957

• DENBURG M.R. (2013)

Vitamin D bioavailability and catabolism in pediatric chronic kidney disease.

Pediatr. Nephrol., 28:1843–1853.

https://www.ncbi.nlm.nih.gov/pubmed/23728936

• COYNE D.W. and  BROWN  AJ. (2012)

Bioavailable vitamin D in chronic kidney disease.

Kidney Int., 82:5–7.

https://www.ncbi.nlm.nih.gov/pubmed/22699377

• THADHANI R.I. (2012)

Bioavailable vitamin D is more tightly linked to mineral metabolism than total vitamin D in incident hemodialysis patients.

Kidney Int., 82:84–89.

https://www.ncbi.nlm.nih.gov/pubmed/22398410