Causes of hypercalcemia in renal transplant recipients: persistent hyperparathyroidism and others.

Hypercalcemia is common in patients after kidney transplantation (KTx) and is associated with persistent hyperparathyroidism in the majority of cases. This retrospective, single-center study evaluated the prevalence of hypercalcemia after KTx. KTx recipients were evaluated for 7 years after receiving kidneys from living or deceased donors. A total of 301 patients were evaluated; 67 patients had hypercalcemia at some point during the follow-up period. The median follow-up time for all 67 patients was 62 months (44; 80). Overall, 45 cases of hypercalcemia were classified as related to persistent post-transplant hyperparathyroidism (group A), 16 were classified as "transient post-transplant hypercalcemia" (group B), and 3 had causes secondary to other diseases (1 related to tuberculosis, 1 related to histoplasmosis, and 1 related to lymphoma). The other 3 patients had hypercalcemia of unknown etiology, which is still under investigation. In group A, the onset of hypercalcemia after KTx was not significantly different from that of the other groups, but the median duration of hypercalcemia in group A was 25 months (12.5; 53), longer than in group B, where the median duration of hypercalcemia was only 12 months (10; 15) (P<0.002). The median parathyroid hormone blood levels around 12 months after KTx were 210 pg/mL (141; 352) in group A and 72.5 pg/mL (54; 95) in group B (P<0.0001). Hypercalcemia post-KTx is not infrequent and its prevalence in this center was 22.2%. Persistent hyperparathyroidism was the most frequent cause, but other important etiologies must not be forgotten, especially granulomatous diseases and malignancies.