In a patient with normal chemistries but elevated calcium, which test is essential to rule out primary causes?

In a patient with normal chemistries but elevated calcium, which test is essential to rule out primary causes?

• A. Plasma vitamin D levels
• B. Serum parathyroid hormone level
• C. Bone density scan
• D. 24-hour urine calcium

Answer: (B)

To determine primary causes of elevated calcium levels in a patient presenting with normal chemistry, measuring serum parathyroid hormone (PTH) levels is essential. This is because one of the most common and critical conditions leading to hypercalcemia is primary hyperparathyroidism, where PTH is secreted excessively due to an adenoma or hyperplasia of the parathyroid glands. When serum calcium is high and PTH is elevated, it indicates primary hyperparathyroidism, while in the presence of high calcium and low PTH, it suggests a non-parathyroid cause (sometimes due to malignancy or vitamin D toxicity). Therefore, assessing PTH levels helps differentiate between these primary causes and directs further management. Other tests like measuring plasma vitamin D levels or conducting a bone density scan can provide additional information on calcium metabolism or bone health but are not essential for ruling out primary causes of hypercalcemia as directly and effectively as serum PTH measurements. A 24-hour urine calcium test can help evaluate renal calcium handling but does not directly assess the primary parathyroid function that is crucial for determining the cause of elevated calcium in this context.

To determine primary causes of elevated calcium levels in a patient presenting with normal chemistry, measuring serum parathyroid hormone (PTH) levels is essential. This is because one of the most common and critical conditions leading to hypercalcemia is primary hyperparathyroidism, where PTH is secreted excessively due to an adenoma or hyperplasia of the parathyroid glands.

When serum calcium is high and PTH is elevated, it indicates primary hyperparathyroidism, while in the presence of high calcium and low PTH, it suggests a non-parathyroid cause (sometimes due to malignancy or vitamin D toxicity). Therefore, assessing PTH levels helps differentiate between these primary causes and directs further management.

Other tests like measuring plasma vitamin D levels or conducting a bone density scan can provide additional information on calcium metabolism or bone health but are not essential for ruling out primary causes of hypercalcemia as directly and effectively as serum PTH measurements. A 24-hour urine calcium test can help evaluate renal calcium handling but does not directly assess the primary parathyroid function that is crucial for determining the cause of elevated calcium in this context.