Primary hyperparathyroidism with normal serum intact parathyroid hormone levels.

To evaluate the features of primary hyperparathyroidism (HPT) with normal serum intact parathyroid hormone (iPTH) levels, we studied 271 consecutive patients undergoing surgery for primary HPT. In 20 patients, serum iPTH levels were within the normal range (10-65 ng/l). In their records, the most common clinical features were fatigue (n=13), polyuria (n=6), renal stone (n=5), and hypertension (n=5). Mean serum calcium and phosphorus were 2.78 and 0.85 mmol/l, respectively: 14 had serum phosphorus within the normal range. Mean serum iPTH was 48.5 ng/l, and was <45 ng/l in nine patients. Cervical ultrasound demonstrated a parathyroid adenoma in nine, and was normal in four. Tc sestamibi parathyroid scintigraphy always demonstrated an adenoma (9/9). In eight patients, normal iPTH values delayed diagnosis. Physicians should be aware of the possibility of HPT in patients with hypercalcaemia, even when serum phosphorus and iPTH levels are within the normal limits. Particularly, HPT cannot be excluded when serum iPTH levels are below the upper part of the normal range. In such cases, cervical imaging, which has the same sensitivity as in other HPT, should be undertaken. These explorations are useful, because many patients are symptomatic and can take advantage of surgery.