The Effect of Short-Term Vitamin D Supplementation on Calcium Status in Vitamin D Insufficient Renal Transplant Recipients at Risk of Hypercalcemia

Abstract

Objective: Vitamin D insufficiency is highly prevalent among renal transplant recipients and in observational studies is associated with adverse outcomes. Hypercalcemia, usually due to persistent hyperparathyroidism, also commonly occurs in this population and often coexists with vitamin D insufficiency. However, concern that vitamin D supplementation might exacerbate the pre-existing hypercalcemia often leads clinicians to avoid vitamin D supplementation in such patients. This feasibility study aimed to quantify the effect on serum calcium of short-term low-dose cholecalciferol supplementation in a group of renal transplant recipients with a recent history of serum calcium levels >10 mg/dL.

Design: A 2-week, single arm, open-label trial.

Setting: Renal transplant follow-up clinic in an Irish University Hospital.

Subjects: Eighteen vitamin D-insufficient adult patients with a functioning renal allograft (estimated glomerular filtration rate > 30 mL/minute/1.73 m²) and a recent history of serum calcium >10 mg/dL.

Intervention: Two weeks of treatment with 1,000 IU cholecalciferol/day.

Main outcome measure: Change in ionized calcium and urine calcium:creatinine ratio at follow-up compared with baseline.

Results: Mean (standard deviation [SD]) baseline 25 (OH) vitamin D (25 (OH) D) concentration was 15.9 (5.97) ng/mL and mean (SD) baseline serum calcium was 10.50 (0.6) mg/dL. Following the 2-week intervention, median (interquartile range [IQR]) change in serum calcium from baseline was -0.08 (-3.6 to 0.08) mg/dL, P = .3. Mean (SD) ionized calcium decreased from 5.24 (0.32) mg/dL at baseline to 5.16 (0.28) mg/dL, P = .05. Median (IQR) change in the urinary calcium:creatinine ratio was 0.001 (-0.026 to 0.299) mg/mg, P = .88. Median (IQR) change in 25 (OH) D was 3.6 (2.9-6.2) ng/mL, P < .05.

Conclusions: In vitamin D-insufficient renal transplant recipients at risk of hypercalcemia, low-dose short-term oral cholecalciferol supplementation improves 25 (OH) D concentrations without exacerbating hypercalcemia or increasing the urinary calcium:creatinine ratio.