Endocrine Abstracts

Background: Hypercalcaemia is defined as an elevated serum calcium level above 2.6 mmol/l and occurs in 1 in 1000 of the population. It commonly results from primary hyperparathyroidism (PHP) which is usually treated with parathyroidectomy. A less common cause of hypercalcaemia is familial hypocalciuric hypercalcaemia (FHH) which is caused by mutations inactivating the calcium-sensing receptor; however FHH is relatively benign and requires no treatment. It is clearly important to distinguish between hypercalcaemia caused by PHP which requires parathyroidectomy, and hypercalcaemia caused by FHH for which no surgery is required. The urine calcium/creatinine clearance ratio (UCCR) is widely used to distinguish between FHH and PHP in patients with hypercalcaemia.

Aim: To determine how reliable the UCCR is in patients with hypercalcaemia to distinguish between FHH and PHP.

Methods: One hundred and three hypercalcaemic patients with a diagnosis of PHP were identified from patients attending our endocrine clinic. A UCCR >0.01 suggested the diagnosis of PHP, and a UCCR <0.01 suggested the diagnosis of FHH. The diagnosis of PHP was further supported by measurement of detectable serum PTH, together with normalisation of serum calcium post-surgery or positive parathyroid histology.

Results: Fifteen percent of patients with hypercalcaemia who were ultimately diagnosed with PHP, had a UCCR <0.01, which falsely suggested the diagnosis of FHH. In patients with hypercalcaemia, a UCCR>0.01 had 84% sensitivity and 85% specificity with respect to the diagnosis of PHP.

Conclusion: This study suggests that the UCCR may fail to reliably differentiate between hypercalcaemia due to PHP and FHH in up to 15% of patients, which could lead to inappropriate management.