In primary hyperparathyroidism, which laboratory finding is typical?

In primary hyperparathyroidism, which laboratory finding is typical?

• A. Phosphate high
• B. Calcium high
• C. PTH low
• D. Vitamin D low

Answer: (B)

Elevated calcium is the hallmark finding in primary hyperparathyroidism. When the parathyroid glands produce too much PTH, several actions raise serum calcium: PTH stimulates bone resorption, releasing calcium into the blood; it increases calcium reabsorption in the kidney’s distal tubule; and it enhances intestinal calcium absorption indirectly by activating vitamin D. The net result is high serum calcium. Phosphate tends to be low in this condition because PTH promotes phosphate wasting in the proximal tubule, so a phosphate high value would be inconsistent with primary hyperparathyroidism. PTH is elevated (not low) in this condition, so a low PTH level wouldn’t fit. Vitamin D status isn’t characteristically low; PTH can increase the active form of vitamin D, so a low vitamin D level isn’t typical.

Elevated calcium is the hallmark finding in primary hyperparathyroidism. When the parathyroid glands produce too much PTH, several actions raise serum calcium: PTH stimulates bone resorption, releasing calcium into the blood; it increases calcium reabsorption in the kidney’s distal tubule; and it enhances intestinal calcium absorption indirectly by activating vitamin D. The net result is high serum calcium.

Phosphate tends to be low in this condition because PTH promotes phosphate wasting in the proximal tubule, so a phosphate high value would be inconsistent with primary hyperparathyroidism. PTH is elevated (not low) in this condition, so a low PTH level wouldn’t fit. Vitamin D status isn’t characteristically low; PTH can increase the active form of vitamin D, so a low vitamin D level isn’t typical.