The influence of parathyroid hormone and its fragments on results from midregion and C-terminal specific radioimmunoassays.
We compared a midregion (44-68) human parathyroid hormone (hPTH) specific radioimmunoassay (M-RIA) with a C-terminal (65-84) hPTH specific radioimmunoassay (C-RIA). The M-RIA discriminated 21 of 23 patients with primary hyperparathyroidism from 95 normals (normal range: 22.4-106.5 pmol/l). With the C-RIA 12 patients including the 2 patients not discriminated by the M-RIA had immunoreactive PTH (iPTH) values within the normal range of this assay (normal range: undetectable to 88.6 pmol/l). To investigate the reasons for these different abilities of separation, hyperparathyroid sera were subjected to gel-filtration and analyzed using the two assays. Intact PTH appeared to have a major influence on the immunoreactivity of circulating PTH in the M-RIA. In contrast, the C-RIA showed the highest immunoreactivity with midregion-C-terminal PTH fragments. Hyperparathyroid sera not discriminated by the C-RIA but with elevated iPTH in the M-RIA showed decreased amounts of midregion-C-terminal PTH fragments, while intact PTH comprised the highest amount of total circulating PTH immunoreactivity in the M-RIA. From the present results we conclude that the superiority of the M-RIA is due to the determination of intact PTH which is preferable for clinical measurements with relation to the diagnosis of primary hyperparathyroidism.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D006961:Hyperparathyroidism / Q000097:blood*; D006962:Hyperparathyroidism, Secondary / Q000097:blood; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood*; D011863:Radioimmunoassay; D012016:Reference Values
D010281:Parathyroid Hormone; D010446:Peptide Fragments; C046385:parathyroid hormone (65-84); C046111:parathyroid hormone (44-68)