Which laboratory pattern is consistent with primary hyperparathyroidism?

• A. Elevated Calcium with Decreased Phosphate and Elevated PTH
• B. Low Calcium with Increased Phosphate
• C. Elevated Phosphate with Normal Calcium
• D. Low PTH with Hypercalcemia

Answer: (A)

Overproduction of parathyroid hormone in primary hyperparathyroidism pushes calcium upward while pulling phosphate downward. PTH increases bone resorption and renal calcium reabsorption, and it promotes phosphate excretion in the kidneys. The net effect is high calcium, low phosphate, and an elevated PTH level. This is the lab pattern you’d expect, so the correct combination is elevated calcium with decreased phosphate and elevated PTH. Other patterns don’t fit this mechanism—for example, low calcium with high phosphate suggests hypoparathyroidism, while high phosphate with normal calcium or other patterns point to different processes.