Diagnostic utility of carboxyl-terminal and intact parathyroid hormone immunoassays in hospitalized patients

In a university-affiliated community hospital, medical records of 58 patients on whom the intact parathyroid hormone immunoassay (I-PTH) and 29 patients on whom both the carboxyl terminal PTH(C-PTH) and I-PTH ordered by physicians were reviewed to determine the reasons for requesting these tests. Reasons for ordering the PTH tests include (1) the evaluation of hypercalcemic patients (25/58 I-PTH); (2) the evaluation of hypocalcemic patients (2/58 I-PTH); (3) to rule out primary hyperparathyroidism in normocalcemic stone formers (4/58 I-PTH, 4/29 C-PTH) and in those with abnormal skeletal x-ray (3/48 I-PTH 1/29 C-PTH); (4) to follow patients with chronic renal failure on dialysis (11/58 I-PTH, 9/29 C-PTH); (5) to rule out ectopic hyperparathyroidism in patients with cancer (2/58 I-PTH, 3/29 C-PTH); (6) to satisfy physicians' intellectual curiosity of patients with diabetes mellitus (3/58 I-PTH, 3/29 C-PTH) and obesity (5/58 I-PTH; 6/29 C-PTH); (7) to evaluate acute renal failure (1/29 C-PTH). In 3/58 patients on whom I-PTH tests were ordered, reason(s) could not be determined. The C-PTH was elevated in 9/9 patients with chronic renal failure, 4/6 obese patients, 2/3 patients with cancer, 1/3 diabetic patients, 1/4 stone formers, 2/2 patients with primary hyperparathyroidism. Patients with chronic renal failure had the highest C-PTH. Based on well established indications for ordering the PTH immunoassays, 25 out of 58 (43%) of I-PTH and 9 out of 29 (31%) of C-PTH ordered are inappropriate.