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