Which condition is most likely to cause high calcium levels in the blood?

High calcium levels in the blood, known as hypercalcemia, are most commonly associated with hyperparathyroidism. This condition occurs when the parathyroid glands produce an excess amount of parathyroid hormone (PTH), which regulates calcium levels in the body. Elevated levels of PTH lead to increased release of calcium from bones, enhanced intestinal absorption of calcium, and increased renal tubular reabsorption of calcium, ultimately resulting in higher calcium levels in the bloodstream.

In contrast, hypoparathyroidism leads to low levels of calcium, as insufficient production of PTH reduces bone resorption and intestinal absorption of calcium. Diabetes insipidus primarily affects water balance and does not directly influence calcium levels. Hypertension is a condition related to high blood pressure and does not have a direct effect on calcium metabolism. Therefore, hyperparathyroidism is the clear condition linked to causing elevated calcium levels.