In primary hyperparathyroidism, what is the expected relationship between serum calcium and PTH?

• A. Hypercalcemia with inappropriately elevated or non-suppressed PTH
• B. Hypocalcemia with elevated PTH
• C. Hypercalcemia with suppressed PTH
• D. Normal calcium with elevated PTH

Answer: (A)

In primary hyperparathyroidism, the parathyroid tissue makes PTH autonomously, so the calcium feedback that normally tames PTH doesn’t work. The result is high calcium in the blood along with PTH that remains inappropriately elevated or non-suppressed for that level of calcium. That combination—hypercalcemia with non-suppressed PTH—is the hallmark pattern.

If calcium is high but PTH is suppressed, that points to a PTH-independent cause of hypercalcemia (like malignancy with PTHrP or vitamin D–related etiologies). If calcium is normal or low with high PTH, that suggests secondary (or tertiary) hyperparathyroidism or other disorders where PTH rises to compensate for low calcium, not primary autonomous secretion.