Review Question - QID 212763

A 47-year-old woman presents to her primary care physician for a wellness checkup. The patient states that she currently feels well and has no complaints. She has failed multiple times at attempting to quit smoking and has a 40 pack-year smoking history. She drinks 4 alcoholic beverages every night. The patient is currently taking a multivitamin and vitamin D supplements. She has also attempted to eat more salmon given that she has heard of its health benefits. Physical exam is notable for back stiffness on mobility testing. The patient states that she frequently has back pain when sitting. Laboratory values are obtained as seen below.

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 12.2 mg/dL
PTH: 75 pg/mL (normal 10 - 65 pg/mL)

Urine:
Color: Yellow
pH: 7.0
Blood: 1+
Protein: Negative
Nitrite: Positive
Bacteria: Positive
Ca2+: Low
Benzodiazepines: Positive

Which of the following is the best explanation for this patient’s electrolyte abnormalities?