Testing for disorders of calcium metabolism.

Assays of serum immunoreactive parathyroid hormone are clinically useful in the differential diagnosis of hypercalcaemic states and in the assessment of the severity of parathyroid bone disease in uraemic patients. Serum immunoreactive calcitonin measurements are essential in the investigation of individuals who might be suffering from medullary carcinoma, and such measurements may be used in the detection of metastases. Serum 25-hydroxyvitamin D assays are useful in patients receiving pharmacological doses of vitamin D, to monitor patient compliance and to prevent the occurrence of vitamin D intoxication. Low values in patients with renal failure and in patients with malabsorption and highly suggestive of the presence of osteomalacia. The measurement of serum levels of dihydroxylated vitamin D metabolites is currently of doubtful clinical relevance, though such measurements may become useful in monitoring patients receiving these compounds therapeutically.