Effect of persistent hypercalcemia on hemoglobin levels after kidney transplantation.

Introduction: After kidney transplantation, persistent hyperparathyroidism commonly occurs, often alongside increased serum calcium levels. It is reasonable to infer that kidney transplant recipients (KTRs) with hypercalcemia related to persistent hyperparathyroidism are more susceptible to developing anemia. However, reports suggest that hypercalcemia could be a contributing factor to erythrocytosis. Our aim was to assess the effect of persistent hypercalcemia on the trajectory of hemoglobin levels after transplantation.

Materials and methods: We conducted a retrospective cohort study investigating the trajectory of hemoglobin in 385 KTRs with and without persistent hypercalcemia (free Ca > 5.2 mg/dL). We performed mixed-model analyses adjusting for potential confounders.

Results: Persistent hypercalcemia was present in 62% KTRs (56% male, median age 36 (IQR 28 - 48) years, median follow-up 4.1 (IQR 1 - 8.2) years). Compared to KTRs without hypercalcemia, KTRs with persistent hypercalcemia had a mean positive difference in hemoglobin levels of +0.76 g/dL/year (95% CI +0.45 - +1.08, p < 0.001) throughout the follow-up period. Specifically, the change slope was +0.80 (95% CI +0.32 - +1.27, p < 0.001) g/dL/year for males and +0.36 (95% CI +0.16 - +1.08, p < 0.001) g/dL/year for females. Persistent hypercalcemia was significantly associated with post-transplant erythrocytosis according to the WHO (47 vs. 24%, OR 2.8, 95% CI 1.8 - 4.4) and altitude-adjusted criteria (22 vs. 10%, OR 2.5, 95% CI 1.2 - 4.5). The effect of hypercalcemia on hemoglobin levels was consistent after adjusting for confounders, except in KTRs who developed an estimated glomerular filtration rate < 45 mL/min/1.73m² after transplantation.

Conclusion: Persistent hypercalcemia after kidney transplantation was significantly associated with higher hemoglobin levels and an increased risk of developing post-transplant erythrocytosis.