Calcium phosphate deposition, tertiary hyperparathyroidism, and the long-term effect on kidney allografts

Background: Tertiary hyperparathyroidism adversely affects kidney allografts, with calcium phosphate deposition hypothesized to be an underlying cause. We analyzed allograft biopsies to investigate risk factors for calcium phosphate deposition and understand its impact on allograft function.

Methods: We reviewed patients who underwent kidney transplantation from 2017 to 2019. Tertiary hyperparathyroidism was defined as an elevated parathyroid hormone and hypercalcemia beyond 3 months' posttransplant or being prescribed cinacalcet. Allograft failure was defined as needing dialysis posttransplantation or retransplantation beyond 3 months' posttransplant. Three- and 12-month allograft biopsies were reviewed for calcium phosphate deposition. The χ², t-test, and multivariate regression were used for statistical analysis.

Results: Of 159 patients who underwent kidney transplantation, 59 (37.1%) were diagnosed with tertiary hyperparathyroidism. Longer preoperative dialysis vintage (odds ratio, 1.47; confidence interval, 1.22-1.80 P < .001) and preoperative cinacalcet usage (odds ratio, 18.4; confidence interval, 7.24-53.0 P < .001) were associated with tertiary hyperparathyroidism. In total, 36 of 59 (61%) patients with tertiary hyperparathyroidism had calcium phosphate deposition on 3- or 12-month kidney allograft biopsy compared with 23 of 100 (23%) patients without tertiary hyperparathyroidism (P < .001). Tertiary hyperparathyroidism (odds ratio, 6.01; confidence interval, 2.91-13.0 P < .001) was associated with calcium phosphate deposition. Calcium phosphate deposition and tertiary hyperparathyroidism were not associated with worse glomerular filtration rate at 3 years' posttransplantation. Of those with data available at 3 years' posttransplantation, 21 of 49 (42.9%) patients remained on cinacalcet. There were 3 of 159 (2%) patients who had allograft failure, 2 of whom had both tertiary hyperparathyroidism and calcium phosphate deposition.

Conclusion: Preoperative variables associated with tertiary hyperparathyroidism included longer dialysis vintage and cinacalcet use. Tertiary hyperparathyroidism was the main risk factor for calcium phosphate deposition posttransplantation. In our population, calcium phosphate deposition and tertiary hyperparathyroidism were not significantly associated with lower glomerular filtration rate.