In hypercalcemia workups, what is the typical relationship between calcium, phosphate, and PTH in primary hyperparathyroidism?

• A. Hypercalcemia with hypophosphatemia and inappropriately elevated or inappropriately normal PTH
• B. Hypercalcemia with hyperphosphatemia and suppressed PTH
• C. Hypocalcemia with high phosphate and elevated PTH
• D. Normal calcium with normal phosphate and normal PTH

Answer: (A)

In primary hyperparathyroidism, the parathyroid glands secrete PTH autonomously, driving calcium up by increasing bone resorption and renal calcium reabsorption while promoting phosphate excretion. Because calcium is already high, PTH should be suppressed, but in this condition it remains inappropriately normal or elevated, indicating PTH-driven hypercalcemia. The renal effect of PTH also lowers phosphate, so you typically see hypercalcemia with hypophosphatemia. This pattern—high calcium, low phosphate, and non-suppressed PTH—best fits primary hyperparathyroidism.