Calcitonin Pre-treatment to Improve SPECT-CT Sensitivity

Inclusion Criteria:

* Diagnosis of primary hyperparathyroidism
* Non-localizing SPECT-CT performed within 365 days prior to consent to participate in study
* Patient desires surgical intervention for treatment of PHPT
* No contraindications to 99mTC-Sestamibi
* No contraindications to treatment with calcitonin
* Serum calcium level prior to non-localizing SPECT-CT is ≥10.5 mg/dL
* Patient consents to participate and undergo second SPECT-CT for purposes of research

Exclusion Criteria:

* Previous surgery to the neck, including resection of parathyroid tissue, except where end organ damage is present and further surgical intervention is medically necessary
* Contraindication to 99mTC-Sestamibi SPECT-CT as evidenced by allergic reaction or adverse event during index SPECT-CT
* Allergy to calcitonin
* Hypocalcemia (contraindication to calcitonin)
* Vitamin D deficiency (contraindication to calcitonin)
* Previous treatment with radioactive iodine
* New prescription of thyroid medication (levothyroxine, armour thyroid tablets, etc. must be taken at time of index scan and research scan)
* Lithium exposure within one year of SPECT-CT (index and research scans)
* Secondary hyperparathyroidism
* Benign familial hypocalciuric hypercalcemia
* Known malignancy, particularly multiple endocrine neoplasia
* New prescription of thiazide diuretic, (thiazide diuretic must have been taken at the time of index scan and second scan)
* Currently taking calcium channel blockers
* Pregnancy