What are the recommended initial investigations for diagnosing hypoparathyroidism in adults?

Recommended initial investigations for diagnosing hypoparathyroidism in adults include:

• Measurement of serum calcium, specifically albumin-adjusted serum calcium, to identify hypocalcaemia (low calcium levels) which is a hallmark of hypoparathyroidism.
• Measurement of serum parathyroid hormone (PTH) levels concurrently with calcium to confirm low or inappropriately normal PTH in the context of hypocalcaemia, which supports the diagnosis of hypoparathyroidism.
• Assessment of serum phosphate, as hypoparathyroidism typically presents with hyperphosphataemia (elevated phosphate levels).
• Measurement of serum 25-hydroxyvitamin D to exclude vitamin D deficiency as a cause of hypocalcaemia and to guide supplementation if needed.
• Additional tests may include renal function tests (e.g., serum creatinine, eGFR) to assess kidney status, as renal impairment can affect calcium and phosphate metabolism.

These investigations help differentiate hypoparathyroidism from other causes of hypocalcaemia and guide appropriate management.