The 4 parathyroid glands are located behind, or sometimes inside of, the thyroid gland. Their job is to maintain calcium levels in the blood at any cost so your muscles can work and your heart can beat. They “borrow” from the calcium reservoir in your bones to accomplish this.
- The glands are extremely sensitive to calcium levels and will respond to low calcium very quickly, and “shut off” when calcium is high.
- We measure parathyroid activity by lab tests for PTH.
What happens if parathyroids are overactive?
- An overactive parathyroid will produce elevated calcium levels.
- When calcium rises significantly patients can feel poorly: abdominal pain, psychological changes, nausea, constipation, and are prone to kidney stones.
- Because the parathyroids are leaching calcium from the bones, those bones become thinner and prone to fractures, which is called osteopenia or osteoporosis.
There are 3 types of hyperparathyroidism:
- Primary hyperparathyroidism – excess (or normal) PTH despite a high calcium. This is a situation where the gland fails to “shut off” and most frequently is caused by 1 oversized parathyroid gland, or an adenoma.
- There is a rare congenital condition called FHH that can mimic this, so testing will be done to evaluate for this as well.
- Secondary hyperparathyroidism – excess PTH with a low (or normal) calcium. Most commonly this occurs in patients with kidney disease, but it can also be caused by low vitamin D or high phosphorus levels. This is treated by finding the underlying cause of excess PTH and fixing that. Otherwise, there is a medication, Cinacalcet, that can “trick” the body into thinking the calcium is already high, and this will reduce PTH.
- Tertiary hyperparathyroidism – excess PTH (usually very extreme elevations) with a high calcium. This occurs when secondary hyperparathyroidism has progressed beyond medical treatment. Usually all 4 glands are enlarged and functioning independently. This is treated by surgical removal of 3 ½ parathyroid glands.
Surgical indications to cure primary or tertiary hyperparathyroidism:
- Age < 50, OR
- Calcium level > 11.5, OR
- 24hr urine calcium level > 400, OR
- Damage to kidneys (stones or decreased function), OR
- Osteoporosis
My calcium is high but my PTH is low, so why is my calcium high?
When the PTH becomes low/undetectable in the setting of high calcium, this is a NORMAL response.We have to look for other reasons, like cancers, medications or certain vitamin toxicities to explain the high calcium.
Resources
Mayo Clinic https://www.mayoclinic.org/diseases-conditions/hyperparathyroidism/
National Institute of Health section on Endocrine Diseases and Hyperparathyroidism
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