What would cause depressed levels of calcium after a thyroidectomy?
The parathyroid glands are located behind the thyroid gland and
are often accidentally removed with the thyroid in a thyroidectomy.
The parathyroid gland makes parathyroid hormone (PTH), which
normally causes an increase in blood calcium levels.
If the parathyroid is lost, so is the PTH, and thus the blood
calcium is lower.