Preoperative treatment of PHPT aims to (1) manage severe and/or symptomatic hypercalcemia and (2) prevent postoperative hypocalcemia. Severe hypercalcemia, defined as a blood calcium level≥3.5mmol/L, requires admission to hospital in a conventional or critical care unit, depending on clinical symptoms and comorbidities. Decision to admit a patient in a critical care unit relies on the existence of one or more clinical manifestations (impaired alertness, dehydration with acute renal failure, severe acute pancreatitis) or threatening electrocardiographic signs, or one or more significant comorbidities, notably cardiovascular. Oral rehydration and/or intravenous volume expansion, adapted to cardiac and renal function, form the basis of treatment to lower blood calcium level. If insufficient, intravenous bisphosphonates (zoledronate or pamidronate) are recommended to achieve a reduction in blood calcium levels sufficiently long to allow surgery to be organized. All bisphosphonate injections must be preceded by a minimum etiological work-up of hypercalcemia, including PTH, phosphate and 25-hydroxy vitamin D levels, as well as calciuria and creatininuria. Since bisphosphonates take 24-36hours to take effect, calcitonin can initially be combined with them, as it has a rapid onset of action of a few hours. Denosumab is recommended in second line where bisphosphonates cannot be used, notably because of impaired renal function. Hemodialysis is proposed for patients with an identified vital risk, especially if volume expansion is not possible due to cardiac or renal insufficiency. Correction of vitamin D deficiency is recommended before parathyroid surgery if blood calcium levels are<
3.5mmol/L, to prevent or attenuate severe postoperative hypocalcemia due to massive calcium transfer to the bone.