Endocrine Abstracts

Background: Parathyroid hormone (PTH) assay is critical for diagnosis of calcium disorders and intraoperative (IO) monitoring of parathyroid surgery. We evaluated the new Access^® Intact PTH (iPTH) on the UniCel^® DxI 800 (Beckman Coulter).

Methods: Imprecision was evaluated for routine and intraoperative (15 min) procedures, at 3 control levels, run 20 times in duplicate over 10 days (NCCLS EP5-A protocol). Normal values were obtained from healthy blood donors (16–66 years; 123 in winter; 163 in summer). Pathological and IO conditions were tested.

Results: For routine assay (iPTH: 30, 291 and 892 pg/ml), intra-assay CVs were 1.9, 1.9, 2.4% and total imprecision was 2.4, 2.6 and 2.4% respectively; for IO procedure (iPTH: 21, 206, 637 pg/ml), intra-assay CVs were 2.0, 2.5, 2.4% and total imprecision 4.4, 4.9, 6.2%, respectively,. iPTH mean normal value was 36 pg/ml (geometrical mean, 95% confidence limits:16–81). iPTH correlated negatively to calcemia (r=−0.25; P<0.001) and 25-OH vitamin D3 (r=−0.29; P<0.001). In winter, iPTH level was 10% higher than in summer (P=0.03), reflecting differences in vitamin D3. Among 35 surgically proven cases of primary hyperparathyroidism (calcium>10 mg/dl), iPTH ranged from 39 to 252 pg/ml (median: 81). iPTH was lower than 3 pg/ml in 2 children with idiopathic hypocalcemia and in 3 patients with malignancy-associated hypercalcemia. In 18 successful surgical procedures for primary hyperparathyroidism, iPTH concentrations fell by 79% (55%–91%) 10 min after ablation, with no further decrease after 20 min. In 1 case of partial removal of an invading parathyroid tumor, PTH decreased by only 22% after 20 min.

Conclusion: The Access^® Intact PTH assay is reliable for diagnostic purposes as well as for intraoperative use, in the setting of a routine core laboratory.