Question

A $35$-year-old woman comes to the clinic for a routine wellness examination. She has no symptoms and feels entirely well. She has no significant past medical history and takes no medications other than an oral contraceptive pill. Her family history is notable for a father who underwent an unsuccessful neck surgery for hypercalcemia of unclear etiology in his twenties. Her vital signs are within normal limits, and the physical examination is unremarkable. Routine comprehensive metabolic panel reveals a serum calcium level of $11.2\text{ mg/dL}$ (normal: $8.4\text{ - }10.2\text{ mg/dL}$) and an albumin level of $4.0\text{ g/dL}$ (normal: $3.5\text{ - }5.0\text{ g/dL}$). A repeat laboratory draw one week later confirms a serum calcium of $11.1\text{ mg/dL}$. A subsequent intact parathyroid hormone (PTH) level is $78\text{ pg/mL}$ (normal: $10\text{ - }65\text{ pg/mL}$) and $25$-hydroxyvitamin D level is $32\text{ ng/mL}$ (normal: $20\text{ - }50\text{ ng/mL}$). Her serum creatinine is $0.8\text{ mg/dL}$. Which of the following is the most appropriate next step in laboratory evaluation?