Circulating molecular forms of parathyroid hormone in primary and secondary hyperparathyroidism

To study the circulating forms of parathyroid hormone (PTH), sera from 5 patients with primary hyperparathyroidism (PHP) and 12 patients with secondary hyperparathyroidism due to chronic renal failure (SHP) were submitted to gel filtration chromatography. The eluent samples were analyzed using two sequence-specific radioimmunoassays (RIA), one amino-terminal (NH2), the other carboxyl-terminal (COOH). The results obtained with the NH2 RIA showed a single molecular form in both groups co-eluting with the intact hormone. The COOH assay identified several molecular forms with a broader distribution in the SHP patients. These results confirm the diagnostic superiority of the NH2 assay under both conditions.