Definitions:
(1) hypocalcemia: serum calcium < 8.0 mg/dL on at least 2 consecutive measurements.
(2) severe hypocalcemia: either (a) serum calcium < 8.0 mg/dL for more than 2 days, or (b) signs of hypocalcemia with paresthesia or positive Chvostek's sign
(3) transient hypoparathyroidism: recovery of parathyroid function within a few weeks to months after surgery
(4) permanent hypoparathyroidism: requirement for vitamin D and/or calcium supplements to maintain eucalcemia 1 year after thyroidectomy, associated with low or undetectable parathyroid hormone levels
Reference ranges for assays used in study:
(1) serum calcium: 8.1-10.4 mg/dL
(2) serum phosphorus: 2.68-4.5 mg/dL
(3) serum parathyroid hormone (PTH), intact molecule assay: 10-55 pg/mL (minimal detection 5 pg/mL)
Risk factors for permanent hypoparathyroidism:
(1) < 3 parathyroid glands preserved in situ during surgery
(2) serum PTH level <= 12 pg/mL (intact hormone assay), performed shortly after surgery (early)
(3) serum calcium <= 8 mg/dL after receiving oral calcium therapy for a week or more (delayed)
(4) serum phosphorus >= 4 mg/dL after receiving oral calcium therapy for a week or more (delayed)
number of risk factors present =
= SUM(risk factors identified)
Interpretation:
• minimum number: 0
• maximum number: 4
• The presence of one or more factors indicates that the patient is at risk for developing permanent hypoparathyroidism.
Follow-up:
• Patients identified as being at risk for permanent hypoparathyroidism should have long-term followup to detect hypocalcemia and to provide appropriate supplemental therapy.
