Rapid calcitriol increase and persistent calcidiol insufficiency in the first 6 months after kidney transplantation

Vitamin D deficiency or insufficiency is prevalent in kidney transplant recipients. Little is known about post-transplantation changes in vitamin D forms, which are essential for bone health and other health outcomes. The aim was to measure the levels of calcidiol and calcitriol during the first 6 months after kidney transplantation and examine their relation with other bone mineral metabolic parameters.

A prospective study was performed on 98 patients recruited between April 2010 and June 2011. Calcidiol and calcitriol levels were measured at baseline and at days 15, 30, 90, and 180 after kidney transplantation.

Serum calcidiol levels remained persistently low: 14.3 (9-22) ng/ml at baseline and 16.3 (10.1-20.6) ng/ml at 6 months (P=0.641). At 6 months, calcidiol levels showed an inverse correlation with simultaneously measured parathyroid hormone levels. Calcidiol showed a trend to be higher in patients transplanted in spring but with no statistically significant difference. Calcitriol levels increased from 17 (13-23.7) pg/ml at baseline to 24 (16-32) pg/ml (P=0.002) in the first 2 weeks after transplantation and reached 37 (25-50) pg/ml (P=0.000) after 6 months. During the follow-up, calcitriol levels showed a significant inverse correlation with baseline fibroblast growth factor-23 levels. At month 6, calcitriol levels were inversely correlated with baseline fibroblast growth factor-23 levels and directly correlated with calcidiol levels.

In most patients, calcidiol levels remain low 6 months after kidney transplantation, whereas calcitriol levels rapidly return to normal. Lower calcidiol blood levels promoted lower calcitriol blood levels and higher parathyroid hormone concentrations.