Endocrine Abstracts

A 61-year-old male was referred for hypercalcaemia. He was experiencing generalized fatigue and underwent several investigations which included serum calcium. He had recently been treated for two episodes of chest infections. At that time, he was also experiencing weight loss and night sweats. His symptoms have since resolved. He had no symptoms of hypercalcaemia- polyuria, polydipsia, abdominal pain, constipation, bone pain, or headaches. He was not taking calcium supplements. He had no chronic illnesses. There was no family history of hypercalcaemia or hyperparathyroidism. Physical examination was normal except for an elevated BMI of 33.6. His initial investigations showed mild hypercalcaemia, hypophosphatemia, and elevated PTH (see table). Urine BJP and serum ACE levels were normal. There were no previous calcium levels prior to his initial presentation to suggest longstanding hypercalcaemia. His bone density scan was normal. Imaging did not show any renal calculi. His calcium: creatinine clearance ratio (CCCR) was 0.0083 which suggested familial hypocalciuric hypercalcaemia. Genetic testing for FHH was negative. At subsequent review, repeat studies show a CCCR of 0.0129 with corresponding serum calcium of 2.83 mmol/l, phosphate 0.68 mmol/l(0.8-1.43), and PTH of 96.3 ng/l. While familial hypocalciuric hypercalcaemia is a rare entity, it is important to differentiate it from primary hyperparathyroidism to prevent unnecessary surgery. There are several clinical features that can be used to discern between the two pathologies, but urinary calcium excretion is primarily used to determine the likely diagnosis and further investigation. However, what are the sensitivity and specificity of this test? Additionally, is there a parathyroid hormone level that makes primary hyperparathyroidism more likely in spite of the calcium creatinine clearance ratio?