Endocrine Abstracts

Background: Hypercalcaemia is common in renal transplant recipients, the majority of whom have PTH-dependent hypercalcaemia due to tertiary hyperparathyroidism. PTH-independent hypercalcaemia is less common and is associated with significant, treatable underlying pathologies. In this study, we aimed to evaluate the prevalence and aetiology of PTH-independent hypercalcaemia in post-renal transplant patients.

Method: This was a retrospective, single-centre biochemical and electronic records audit of renal transplant recipients treated at the renal unit of the Royal London Hospital. Inclusion criteria included patients with renal transplants performed between January 1972 and January 2022. Patients with inadequate records were excluded. A corrected serum calcium of ≥2.6 mmol/l, occurring any time after 3-months post-transplant, was used to determine prevalence of hypercalcaemia. A PTH value of <1.6 pmol/l was used to define PTH-independent aetiology.

Results: 1876 renal transplant recipients were studied, including 484 patients who had a functioning graft within 12 months of their death. The prevalence of post-renal transplant hypercalcaemia was 41.2%. 5.2% of patients with hypercalcaemia had a suppressed PTH. Of these, 23.7% had transient hypercalcaemia in the context of calcium and activated vitamin D replacement following pre-transplant parathyroidectomy. In all cases, the calcium normalised on adjustment of their oral calcium/vitamin D replacement. Opportunistic infection accounted for 21.1% of PTH-independent hypercalcaemia cases, which included PJP and Aspergillus infections. 18.4% had an underlying malignancy, the commonest of which were Renal Cell carcinoma of the native kidney and PTLD. 2.6% of patients had Sarcoidosis. 15.8% had concurrent, unrelated infections. The aetiology of hypercalcaemia remained unknown in 18.4% of patients. Hypercalcaemia improved in all cases after hydration and treatment of the underlying aetiology. A statistically significant increase in kidney function occurred 6-months after correction of hypercalcemia (r=0.7722; P<0.0001).

Conclusion: PTH-independent hypercalcaemia in renal transplant patients is rare, but is associated with significant underlying pathology, including malignancy and infection.