Normocalcemic hyperparathyroidism in patients with osteoporosis.

Background: Diagnosing primary hyperparathyroidism (PHP) in patients with osteoporosis is important because of the benefits of surgery. Screening patients with osteoporosis for PHP with only total serum calcium level will fail to diagnose PHP in patients with intermittent or no elevation of the total calcium level.

Methods: This is a retrospective study of 140 patients who had a preoperative bone density study of the 223 patients who had surgery for PHP from January 1995 to June 1999. Normocalcemic hyperparathyroidism was defined as having all normal total calcium values or only intermittent elevation defined as at least 40% of the total calcium values in the normal range.

Results: Osteoporosis was identified in 64 of these 140 patients (46%). Fifteen patients with osteoporosis and PHP had normocalcemic hyperparathyroidism. Six of these patients had all preoperative total calcium values in the normal range, and the remaining 9 patients had intermittent elevation of the total calcium. This group consisted of 12 women and 3 men aged 55 to 79 years. Forty-four concomitant ionized and total calcium values were available in the patients with all normal preoperative total serum calcium values. Forty-two serum ionized calcium values (95%) were elevated. Fifty-one concomitant values were available in the patients with intermittent elevation of the total calcium, and only 20 total calcium values (39%) were elevated and 47 of ionized values (92%) were elevated ( P < .01). Intact parathyroid hormone was also significantly better than total calcium in identifying PHP. Twenty of 23 intact serum parathyroid hormone values (87%) were elevated ( P < .05).

Conclusions: Screening patients with osteoporosis for PHP with only total calcium levels will fail to identify patients with no elevation of total calcium level and many patients with only intermittent elevation of the total calcium level. Ionized calcium and intact parathyroid hormone were comparable and significantly better than total calcium level in the detection of PHP in patients with osteoporosis. Ionized calcium and intact parathyroid hormone should be used to diagnose hyperparathyroidism in patients with osteoporosis and normal serum total calcium levels.