Immunoreactive parathyroid hormone in early and advanced renal failure.

Immunoreactive parathyroid hormone (iPTH) was measured in the serum of 20 patients with early renal failure (ERF) using three assays with different specificity. Half of these patients had elevated iPTH in one or more assays, up to twice the upper limit of normal. In contrast, 36 patients with a creatinine clearance below less than 20 ml/min had an 80% elevated iPTH, up to 5 times the upper limit of normal. The patients with ERF and elevated iPTH had a lower serum calcium but no higher serum phosphate than those with normal iPTH. The differences in iPTH in early and end-stage renal failure can be explained by known differences in metabolism of different PTH forms in uremia.