Significance of parathyroid hormone (PTH) radioimmunoassay in the diagnosis of primary hyperparathyroidism: an experience based on 63 surgically proven cases.

Abstract

The significance of PTH-radioimmunoassay was assessed in 63 surgically proven cases of primary hyperparathyroidism. To detect hyperparathyroidism, an increase in the free serum Ca index, [1-(8 X Alb + 2 X Glb + 3)/100] X Ca, has the highest predictive value (100%) for a positive test but a low predictive value (11.8%) for a negative test. It was necessary to improve the criteria to rule out the diagnosis of hyperparathyroidism. We therefore carried out a PTH radioimmunoassay employing kits made by CIS. The criteria for ruling out the diagnosis of hyperparathyroidism were that free serum Ca index was lower than 3 and PTH was lower than 4 mU/ml. The predictive value of these criteria for ruling out the diagnosis was 83.3%, significantly greater than the previously described criteria. Furthermore, the PTH concentration was significantly correlated to the weight of pathological parathyroid tissue surgically excised and to the free serum Ca index, although to a lesser extent than the latter. Thus, PTH-RIA is of value in improving diagnostic accuracy and in determining the severity of the disease.