Final answer:
The most common cause of hypercalcemia in outpatients is primary hyperparathyroidism, though malignancies like multiple myeloma can also cause it.
Step-by-step explanation:
The most common cause of hypercalcemia in an outpatient setting is often related to primary hyperparathyroidism. This condition occurs due to the overproduction of parathyroid hormone (PTH) by the parathyroid glands, which are located in the neck.
Primary hyperparathyroidism frequently results from a benign tumor or enlargement of one or more of the parathyroid glands, leading to excessive secretion of PTH. Elevated levels of PTH cause increased calcium release from bones and increased reabsorption of calcium from the kidneys, resulting in high levels of calcium in the blood (hypercalcemia).
Other potential causes of hypercalcemia in outpatient settings may include:
1. **Medication-induced:** Certain medications, such as thiazide diuretics, lithium, excessive vitamin D or calcium supplementation, and others, can lead to elevated calcium levels.
2. **Chronic kidney disease:** Impaired kidney function can result in decreased excretion of calcium, leading to hypercalcemia.
3. **Malignancy:** Some cancers, particularly those affecting the bones, can cause an increase in blood calcium levels due to bone breakdown or the release of substances that affect calcium metabolism.
4. **Vitamin D toxicity:** Excessive intake of vitamin D supplements can lead to increased absorption of calcium from the intestines, resulting in hypercalcemia.
5. **Hyperthyroidism:** Although less common, overactive thyroid function can lead to increased bone turnover and subsequent hypercalcemia.
When assessing a patient with hypercalcemia, a thorough medical history, physical examination, and further laboratory tests, including measurement of PTH, vitamin D levels, kidney function, and other relevant investigations, are essential for determining the underlying cause. Treatment depends on the specific cause identified and may involve addressing the underlying condition, modifying medications, or other targeted interventions as necessary.