What initial laboratory tests should I order to confirm a diagnosis of primary hyperparathyroidism in a patient with elevated calcium levels?

Initial laboratory tests to confirm primary hyperparathyroidism in a patient with elevated calcium levels include:

• Measure albumin-adjusted serum calcium to confirm hypercalcaemia (≥2.6 mmol/L) and repeat the measurement at least once if elevated (≥2.6 mmol/L or ≥2.5 mmol/L with symptoms) to verify persistence.
• Measure parathyroid hormone (PTH) concurrently with albumin-adjusted serum calcium if calcium is ≥2.6 mmol/L on at least two occasions, or ≥2.5 mmol/L with suspicion of primary hyperparathyroidism, using a random blood sample.
• Do not measure ionised calcium for diagnosis in primary care.

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