↑ PTH, ↑ Ca²⁺ → 1° hyperparathyroidism (eg, hyperplasia, adenoma, carcinoma)

↑ PTH, ↓ Ca²⁺ → 2° hyperparathyroidism (eg, chronic renal failure, vitamin D deficiency, ↓ Ca²⁺ intake)

↓ PTH, ↓ Ca²⁺ → 1° hypoparathyroidism (eg, surgical resection, autoimmune)

↓ PTH, ↑ Ca²⁺ → PTH-independent hypercalcemia (eg, excess ↑ Ca²⁺ intake, cancer, ↑ vitamin D)