Which laboratory tests are essential for confirming a diagnosis of osteomalacia?

To confirm a diagnosis of osteomalacia, essential laboratory tests include measurement of serum 25-hydroxyvitamin D (25[OH]D) to assess vitamin D status, serum adjusted calcium to detect hypocalcaemia or hypercalcaemia, serum phosphate, and alkaline phosphatase levels. Elevated alkaline phosphatase with low or normal calcium and phosphate levels supports the diagnosis. Additionally, parathyroid hormone (PTH) measurement is important to evaluate secondary hyperparathyroidism, which commonly occurs in osteomalacia. Urinary calcium excretion tests may be considered to exclude other metabolic bone diseases. These tests together help differentiate osteomalacia from other causes of bone pain and fragility fractures NICE CKS[Song 2017].

Specifically, serum 25(OH)D below 50 nmol/L indicates vitamin D deficiency, a common cause of osteomalacia, and should prompt assessment of calcium and phosphate metabolism NICE CKS. Alkaline phosphatase is typically elevated due to increased osteoblastic activity in defective bone mineralization [Song 2017]. Serum phosphate is often low or normal, reflecting impaired bone mineralization. PTH is usually elevated as a compensatory response to hypocalcaemia or vitamin D deficiency NICE CKS. Measuring adjusted serum calcium is critical to detect hypocalcaemia or hypercalcaemia, which may influence management and indicate alternative diagnoses NICE CKS.

In summary, the essential laboratory panel for confirming osteomalacia includes serum 25(OH)D, adjusted calcium, phosphate, alkaline phosphatase, and PTH. This integrated approach aligns with UK clinical guidelines and is supported by biochemical indices described in recent literature [Song 2017]NICE CKS.