Which statement best distinguishes primary hyperparathyroidism from tertiary hyperparathyroidism?

Which statement best distinguishes primary hyperparathyroidism from tertiary hyperparathyroidism?

• A. Primary hyperparathyroidism is autonomous PTH secretion from the parathyroids; tertiary hyperparathyroidism is autonomous PTH secretion after prolonged secondary hyperparathyroidism (e.g., in CKD)
• B. Primary hyperparathyroidism is due to PTH resistance; tertiary hyperparathyroidism is due to pituitary adenoma
• C. Primary hyperparathyroidism arises after CKD; tertiary hyperparathyroidism occurs with familial hypocalciuria
• D. Primary hyperparathyroidism causes hypocalcemia; tertiary hyperparathyroidism causes hypercalcemia

Answer: (A)