Clinical value of calcium load test in differential diagnosis of different types of hyperparathyroidism

To investigate the clinical value of calcium load test in the differentiation of various types of hyperparathyroidism (HPT).

A total of 56 healthy subjects (Control) and 68 patients with different types of HPT hyperparathyroidism were recruited into this study.

In primary HPT (PHPT) group, the inhibition rate of PTH (PTH-IR) was significantly smaller than those in Control, SHPT1 and CuHPT group (all P = 0.000). There was no significant difference in the PTH-IR among Control, mild secondary HPT (SHPT1) and cause-unknown HPT (CuHPT) group. In severe secondary HPT (SHPT2) group, the PTH-IR was significantly smaller than those in Control (P = 0.005), SHPT1 (P = 0.001) and CuHPT group (P = 0.002), but was similar to that in tertiary HPT (THPT) group (P = 0.644). ROC curve showed PTH-IR of < 71.26% could differentiate PHPT patients from controls; PTH-IR of < 82.26% could differentiate PHPT patients from SHPT1 patients; PTH-IR of < 82.60% could differentiate SHPT1 patients from SHPT2 patients.

Calcium load test could effectively differentiate mild PHPT patients from mild SHPT patients and healthy subjects. In SHPT patients, the autonomous tendency of the parathyroid gland gradually increases with the deterioration of impaired renal function, resulting in similar parathyroid response to calcium between severe SHPT and THPT. The autonomous property of the parathyroid gland may become one of the indications for parathyroidectomy in SHPT patients.