Hypocalcemia after thyroidectomy

Serum calcium, sodium, potassium, chloride, magnesium, phosphorus, osmolarity, total protein, albumin, parathyroid hormone, and calcitonin values were systematically surveyed in 135 patients who underwent thyroidectomy and in 104 control surgical patients. A transient and moderate hypocalcemia developed after operation in thyroidectomized and control patients. Concentrations of other electrolytes, osmolarity, proteins, and albumin followed the same pattern of evolution. After thyroidectomy, the degree and duration of hypocalcemia increased with the extent of thyroid resection. A profound hypocalcemia (less than 2.0 mmol/L) and a marked reduction of the parathyroid hormone concentration (below normal) were present in 12% and 8% of cases after subtotal thyroidectomy and in 22% after total thyroidectomy. Calcitonin values did not increase after thyroidectomy. A slight correlation was observed between the preoperative serum alkaline phosphatase level and the minimal postoperative serum calcium level. It is concluded that post-thyroidectomy hypocalcemia is a multifactorial phenomenon. It is due, at least in part, to hemodilution. A temporary parathyroid insufficiency after subtotal and total thyroidectomy, and an avidity of the skeleton for calcium in hyperthyroid patients, may aggravate the hypocalcemia.