Preoperative Normal Level of Parathyroid Hormone Signifies an Early and Mild Form of Primary Hyperparathyroidism

Abstract

Contemporary patients are often diagnosed with mild or intermittent hypercalcemia. In addition, most studies demonstrate patients with parathyroid (PTH) levels in the upper normal range. The aim of the present investigation was to define subgroups of patients with mild primary hyperparathyroidism (pHPT), which could be of importance in the decision for or against surgical treatment. Two-hundred and eleven patients, operated for pHPT were investigated with biochemical variables known to reflect PTH activity, renal function, and bone mineral content. The preoperative diagnosis of pHPT was based on the presence of hypercalcemia combined with an inappropriate serum concentration of PTH. The mean age of the patients was 64 ± 14 years and the mean serum level of calcium was 2.78 ± 0.19 mmol/L. One hundred and sixty-two patients (77%) had raised levels of calcium and PTH the day before surgery (overt pHPT), 25 patients (12%) had a normal level of calcium and a raised PTH level (normal calcium group), and 20 patients (9%) had a raised level of calcium and a normal level of PTH (normal PTH group). In four patients the level of calcium and PTH was normal. Between-group analysis demonstrated no major difference in symptom and signs of pHPT. Except for lower adenoma weight, patients in the normal calcium group did not essentially differ from the patients in the overt pHPT group. However, patients in the normal PTH group were a decade younger, and had better renal function, lower bone turnover, and a preserved bone density compared with patients in the overt pHPT group. In conclusion, the data from the present investigation show that pHPT patients with a preoperative normal PTH level have an early and mild form of the disease. Furthermore, the serum calcium concentration does not reflect disease severity in pHPT.