The predictive value of laboratory findings in patients with primary hyperparathyroidism

Despite extensive preoperative imaging and intraoperative "gadgetry" to facilitate localization of abnormal parathyroid glands, the onus of identification and resection remains with the surgeon in the operating room. We pondered the relative usefulness of routine laboratory studies to the surgeon as predictive guides to the intraoperative findings in patients with primary hyperparathyroidism (HPT).

Pre- and postoperative laboratory data were analyzed in 166 consecutive patients (1998 to 1999) undergoing successful cervical exploration for sporadic primary HPT and were correlated with the pathologic findings. Patients with secondary HPT, multiple endocrine neoplasia, familial HPT, and parathyroid carcinoma were not included in this study.

One hundred eighteen women and 48 men (mean age = 63 years) with parathyroid adenoma (n = 155) and sporadic hyperplasia (n = 11) were evaluated. Mean parathormone (PTH) levels varied little with the pathology: adenoma = 9.6 pmol/L and hyperplasia = 10.2 pmol/L (p > 0.05). In patients with parathyroid adenoma, analysis of preoperative measures showed a positive correlation (r = 0.48, p < 0.0001) with PTH and gland weight. The correlation appeared to be the strongest in the tails of the distribution; in 22 of 23 (96%) cases with PTH levels lower than 6 pmol/L, the offending lesion or lesions were less than 400 mg; in all six cases with PTH levels higher than 18.0 pmol/L, the abnormal gland or glands weighed more than 800 mg. PTH levels between 6 and 18 pmol/L revealed mean adenoma weight of 757 mg (median = 420 mg; range = 50 to 5,500 mg).

Extreme values of PTH in patients with single-gland parathyroid disease alert the surgeon to the likelihood of small or large parathyroid adenomas. Laboratory studies do not differentiate adenoma from hyperplasia, nor do they pinpoint the size of abnormal glands with moderate-range PTH values.