A parathyroid scan is an exam to determine the function and health of the parathyroid gland which regulates calcium uptake in the body.

This type of scan is called a sestamibi scan, after the tiny protein molecule that attaches to active parathyroid tissue in this test and that is injected into the blood stream as the first step in the test.  Bound to a safe, low-level radioactive substance, this protein accumulates in abnormal parathyroid tissue and is then easily imaged by a detector that creates a nuclear-medicine image of any activity present in the parathyroids.  (Note that normal parathyroid glands become dormant when blood calcium is high; thus, in the presence of an abnormal parathyroid gland, normal parathyroid glands are inactive and will not absorb the radioactive material and, therefore, do not become radioactive and, as a result, remain invisible on the scan.)  An overactive parathyroid will show up as bright, radioactive spot.

By knowing which of the four parathyroid glands is hyperfunctioning, a surgeon is able to remove only the one parathyroid gland that is producing excessive amounts of parathyroid hormone and no longer under the biochemical control of the body, and leave the other 3 normal parathyroid glands in place.