Normocalcaemic primary hyperparathyroidism (nPHPT) is a form of parathyroid overactivity where parathyroid hormone (PTH) is raised but blood calcium stays in the normal range on repeated tests. This can be confusing, because people often expect high calcium if there is a parathyroid problem.
Your four parathyroid glands sit behind the thyroid in your neck and help keep calcium at a healthy level. When calcium falls, they release PTH, which acts on bone, kidney and, via vitamin D, the gut to raise calcium. In primary hyperparathyroidism, one or more glands become overactive and make too much PTH.
In nPHPT, tests show:
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Persistently high PTH
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Normal total and ionised calcium
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No other clear reason for the high PTH
Before making this diagnosis, we must rule out “secondary” causes of high PTH, such as low vitamin D, low calcium intake, gut absorption problems (for example coeliac disease or after bariatric surgery), chronic kidney disease, urinary calcium loss, and some medicines (for example lithium, certain diuretics, osteoporosis and anti‑seizure drugs).
Many people with nPHPT feel well. Others are found to have low bone density or osteoporosis, and some have kidney stones. It is still being studied how often nPHPT progresses to the “classic” picture with high calcium; many people remain stable, while a minority develop high calcium over time.
Management usually involves careful monitoring: regular blood tests for calcium, vitamin D, and kidney function, and bone density scans every 1–2 years. Surgery (parathyroidectomy) is generally reserved for people with clear bone or kidney complications or those who later develop high calcium.
