This is a great question.

Short answer: your 4th parathyroid gland is likely not completely normal. But that doesn’t mean it will cause problems. I would recommend following calcium levels annually, just as I recommend for other parathyroid patients.

Long answer: First let’s review what you had done. You had parathyroid surgery for primary hyperparathyroidism, and during the operation your surgeon saw three diseased glands and removed those. While it is theoretically possible to have three parathyroid adenomas (benign tumors) and have one normal parathyroid gland, it is extremely unlikely. It is much more likely that all four glands are diseased, which is called hyperplasia. This is just a different form of primary hyperparathyroidism, which occurs in over 10% of patients with primary hyperparathyroidism.

Even if your fourth gland looked pretty good, it was likely diseased. When I see hyperplasia, it usually is not the case that all four parathyroid glands look equally bad. In fact, sometimes one gland will actually look pretty normal. The treatment for hyperplasia usually is removing three glands and part of the fourth. If the fourth looks normal in size, then you don’t need to remove much at all of it.

But what happens to that gland that you leave in? By definition, with hyperplasia that gland is not normal. But if it is small, then it won’t be capable of overproducing PTH. As long as it is making some PTH, but not too much, your calcium level will stay in the normal range. Over time (years), the gland may grow and start to produce more PTH. This would show as a rise in your calcium level. At that point, sometimes we need to reoperate and remove a portion of the remaining gland. Usually, though, a reoperation is never necessary. The gland continues to make a normal amount of PTH and the calcium stays normal.

I recommend watching your calcium and checking it annually, but I wouldn’t worry about that last gland unless you see the calcium go high again.

Vitamin D helps your intestines absorb calcium, so it helps regulate your blood calcium levels. If your calcium drops to low, it will stimulate your remaining parathyroid gland. This is why taking Vitamin D helps keep the PTH down - it helps absorb calcium, so the parathyroid gland does not have to work as hard to get the calcium level up. You should try to keep your calcium in the mid to high 9s. If it is in the low 9s or lower, then your parathyroid will start making more hormone, and bulking up (which you don’t want).

Right now, if your calcium level is normal, you don’t need to worry about that last gland.