What initial blood tests should I order to confirm a diagnosis of primary hyperparathyroidism in a patient with hypercalcemia?

Initial blood tests to confirm a diagnosis of primary hyperparathyroidism in a patient presenting with hypercalcemia include:

• Measure albumin-adjusted serum calcium to confirm hypercalcemia, ensuring the level is 2.6 mmol/litre or above on at least two separate occasions.
• Measure parathyroid hormone (PTH) concurrently with albumin-adjusted serum calcium if the calcium level is 2.6 mmol/litre or above on at least two occasions, or 2.5 mmol/litre or above with clinical suspicion of primary hyperparathyroidism.
• Do not measure ionised calcium for this diagnosis.

These tests establish the biochemical diagnosis of primary hyperparathyroidism by demonstrating elevated calcium with inappropriately normal or raised PTH levels.