Can the volume of abnormal parathyroid tissue be predicted by preoperative biochemical measurement?

A strong correlation between the biochemical manifestations of hyperparathyroidism and the volume of abnormal parathyroid tissue could be used to guide the extent of surgical exploration and parathyroid gland resection (i.e., finding a small "adenoma" in a patient with marked hypercalcemia would dictate further exploration). We examined this relationship in patients for whom data were collected prospectively (n = 14) and retrospectively (n = 27). We considered only patients cured after excision of a single gland and glands for which a three-dimensional description or volume of water displacement was available. To exclude artifactually elevated serum concentrations of parathyroid hormone (PTH), PTH values were used only from patients with levels of serum creatinine less than 2 mg/dl. To accommodate different assays, highest preoperative PTH, ionized calcium, and alkaline phosphatase (AP) values were expressed as percent above upper normal limit. There was excellent agreement (r = 0.93, p less than 0.05) between measured and calculated gland volume. In the prospective study (but not in the retrospective study) there was a significant (p less than 0.05) correlation (r = 0.61) between gland volume and highest preoperative total calcium value; however, there was considerable variation in gland size in patients with similar calcium levels. In neither study was there a significant correlation between gland volume and any of the following: calcium, ionized calcium, midregional PTH, carboxyterminal PTH, or intact PTH, alkaline phosphatase, and urine cyclic adenosine monophosphate (AMP). In the prospective study there was a tendency for urine cyclic AMP, ionized calcium, and AP to increase with increasing gland volume (r = 0.42, 0.45, and 0.51, respectively). Preoperative measurements of calcium, PTH, urine cyclic AMP, and AP are too inconsistent to rely on for determining the extent of parathyroid gland resection.