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 hyperphosphatemia (elevated phosphate levels).
• Measurement of serum magnesium, since hypomagnesemia can cause functional hypoparathyroidism and should be corrected.
• Vitamin D levels should be measured to exclude vitamin D deficiency as a cause of hypocalcaemia.

These tests are essential to differentiate hypoparathyroidism from other causes of hypocalcaemia and guide further management.