This patient's urine calcium and creatinine levels should be measured. Her laboratory values are consistent with hypercalcemia, and her parathyroid hormone level is toward the upper end of the normal range. In her age group and with a family member with a suspicious history, it is important to distinguish between primary hyperparathyroidism and familial hypocalciuric hypercalcemia (FHH). The distinction between primary hyperparathyroidism and FHH can be made by a 24-hour urine collection for calcium and creatinine, which will establish the amount of kidney calcium excretion and will allow evaluation of the calcium-creatinine ratio. Total urine calcium of less than 200 mg/24 h (5 mmol/24 h) and a calcium-creatinine ratio less than 0.01 are highly suggestive of familial hypocalciuric hypercalcemia. FHH results from a mutation in a specific calcium-sensing receptor in the parathyroids and kidneys, and results in an upward shift in the range of calcium and PTH leading to these clinical findings. Although a rare entity, making this diagnosis is crucial because it may prevent unnecessary parathyroidectomy for the patient. The course of FHH is rarely associated with hypercalcemia and therefore does not require therapy to lower serum calcium levels. Screening other family members for the disorder is indicated.

Bone densitometry is not indicated in this age group in the absence of fragility fractures or other risk factors such as long-term high-dose glucocorticoid use or primary hyperparathyroidism.

A parathyroid sestamibi scan is a very useful nuclear imaging study for localization of adenomas in patients with primary hyperparathyroidism or parathyroid cancer. However, primary hyperparathyroidism has not been confirmed in this patient with suspicion for FHH, making this study premature.

The need for surgical treatment in this patient has also not been established. Therefore, surgical referral for parathyroidectomy would not be appropriate.