Isolated hypophosphataemia as an early marker of primary hyperparathyroidism

Summary Primary hyperparathyroidism (PHPT) is a disease caused by overactive parathyroid glands with consequent hypercalcaemia. The main cause in 85–90% of the cases is the presence of a solitary parathyroid adenoma. The most common presentation is with asymptomatic hypercalcaemia diagnosed on routine biochemical testing. Although low serum phosphate levels are an associated finding in primary hyperparathyroidism, the diagnostic criteria for PHPT remain to be hypercalcaemia, high or inappropriately normal PTH and hypercalciuria. This case report presents a patient who presented with low phosphate levels without any other biochemical evidence of PHPT, who returned several years later with overt primary hyperparathyroidism. This report intends to raise interest among the medical fraternity whether there is a need to consider hypophosphataemia as an early sign of PHPT. Learning points Primary hyperparathyroidism is a relatively common condition with varying clinical and biochemical presentation. The most common presentations still remain as an asymptomatic biochemical abnormality closely related to calcium, PTH and bone metabolism. Not much attention is usually given to associated biochemical abnormalities, and hence they are usually less investigated. Further research is needed to establish if patients need long-term monitoring when no obvious cause for isolated hypophosphataemia has been found.