Radioimmunoassay of carboxyl and amino terminal fragments of parathyroid hormone for the evaluation of secondary hyperparathyroidism in chronic renal failure

ABSTRACT

1. Some parameters of calcium and phosphorus metabolism and the radioimmunoassay of plasma concentrations of both the carboxyl (COOH) (residues 53-84) and amino (NH2) terminal (residues 1-34) fragments of parathyroid hormone (PTH) were measured to evaluate secondary hyperparathyroidism in 68 patients with chronic renal falure (CRF), 34 of whon were on hemodialysis therapy. 2. The upper limits of the normal values for serum PTH-NH2 and PTH-COOH concentrations were 28 and 146 pmol/l, respectively. Patients with mild CRF (plasma creatinine (CRp) 1.2-2 mg/dl) hadh normal mean serum total calcium, low mean phosphorus, undetectable plasma levels of PTH-COOH concentration and normal fractional excretion of phosphorus (FEP). Patients with moderate CRF (CRp2.1-4 mg/dl) had normal mean serum concentrations of both total calcium and phosphorus, and elevated mean levels of both plasma PTH-COOH and PTH-NH2 associated with increased FEP. Patients with end-stage CRF (CRp > 4mg/dl) and those on hemodialysis had elevated mean serum phosphorus levels and decreased mean serum total calcium concentrations compared with those with mild and modetate CRF, and more pronounced, increases in both mean plasma PTH-COOH and PTH-NH2. 3. The logarithm of plasma PTH-NH2, but not PTH-COOH, concentration correlated positively with FEP and serum phosphorus concentration and negatively with total serum calcium concentration, while the logarithms of both PTH-NH2 and PTH-COOH levels correlated positively with CRp. 4. Calcium infusion (2 mg Kg-1 h-1 for 90 min) in eight patients with high plasma levels of PTH-NH2, and PTH-COOH resulted in a significant decrease of plasma PTH-NHL but not of plasma PTH-COOH concentration. 5. These data demonstrate increased plasma PTH levels in moderate renal failure and suggest that the assay of plasma PTH-NH2 rather than PTH-COLL is more appropriate for the evaluation of secondary hyperparathyroidism in chronic renal failure