Thanks for reaching out. A calcium of 10.4 mg/dl is high for your age. Most of the time, a high calcium level is caused by primary hyperparathyroidism.

Certain cancers, including breast cancer, can also cause high calcium, but this is much less common. Fortunately, it is easy to determine whether the high calcium is caused by parathyroid disease or something else, by checking the parathyroid hormone (PTH) level.

When high calcium is caused by cancer, PTH levels will be suppressed. That is, the PTH will be very low, under 20 pg/ml (or 2.1 pmol/L). If the PTH is not in the suppressed range, then primary hyperparathyroidism is the most likely explanation for the high calcium.

If your calcium is high and the PTH is suppressed, you will need further workup to determine the cause of the high calcium. If your calcium is high (above 10.0 mg/dl for your age) and the PTH is in the normal or elevated range, then you likely have primary hyperparathyroidism.

The next step, then, is to ask your doctor to check calcium and PTH levels together. It can also be helpful to check Vitamin D levels, particularly if you are taking Vitamin D. High doses of Vitamin D (such as 5000 units daily) can also cause high calcium.