Use of Calcium and Parathyroid Hormone Nomogram to Distinguish Between Atypical Primary Hyperparathyroidism and...

The diagnosis of primary hyperparathyroidism (1°HP) has become more complex, as fewer patients present with classic phenotype of concomitant elevation of calcium and parathyroid hormone (PTH). In addition, the distinction between normal versus abnormal patients is challenging, with an increasing number of patients with 1°HP, who have calcium and/or PTH values within the "reference" range. Patients with "inappropriately" elevated PTH values relative to their serum calcium are considered to have 1°HP.

The study population consisted of 1753 patients with pathologically proven 1°HP and 74 healthy control patients. Nomograms were created by plotting PTH versus calcium of the two groups. The 95 % confidence zone of calcium and PTH for normal individuals was plotted and compared to patients with 1°HP.

The comparison of control and disease groups showed a clear demarcation zone on the plots of calcium versus PTH. In the group of 1°HP, 70 % had classic 1°HP presentation with the concomitant elevation of both calcium (≥10.5 mg/dL) and PTH (≥65 pg/dL). 21 % had "normocalcemic" HP with calcium ≤10.5 mg/dL and PTH ≥65 pg/dL. 6 % had "normohormonal" HP with calcium ≥10.5 mg/dL and PTH ≤65 pg/dL. 3 % had both calcium and PTH within the reference range. 68.5 % of patients had single adenoma, 16 % double adenoma, and 15.5 % hyperplasia.

This nomogram serves as a diagnostic tool to distinguish normal patients from those with 1°HP, particularly those with atypical presentations. This recognition would permit previously observed patients to benefit from curative surgery.