Parathyroid hormone in chronic renal failure: studies with two different parathyroid hormone radioimmunoassays

Two assays for immunoreactive parathyroid hormone (iPTH) with different specificities were used to evaluate the role of iPTH measurement in patients with chronic renal failure (CRF). One measured largely C-terminal iPTH fragments, the other largely intact iPTH. In untreated CRF, the log iPRH for each assay was significantly correlated with the reciprocal of the creatinine clearance (CCr). C-terminal iPTH was elevated at relatively high CCr values, but intact iPTH was not elevated until later in the progression of CRF. In hemodialysis patients treated with 25-hydroxyvitamin D3, intct iPTH correlated better than C-terminal iPTH with clinical improvement. These two assays used together were more helpful in evaluation of CRF patients than either assay alone.