title: Immunoreactivity of plasma parathyrin-related peptide: three region-specific radioimmunoassays and a two-site immunoradiometric assay compared.
abstract: We measured parathyrin (parathyroid hormone)-related peptide (PTHRP) in plasma by three region-specific RIAs and compared them with an established two-site immunoradiometric assay (IRMA) of PTHRP1-86 in samples from control subjects and from patients with primary hyperparathyroidism (PH) and humoral hypercalcemia of malignancy (HHM). The two direct RIAs of PTHRP1-34 and PTHRP37-67 were specific for regions 9-18 and 52-61, respectively. In the extraction RIA of PTHRP1-34 we used an affinity gel containing a monoclonal antibody specific for the 17-27 sequence; cross-reacting PTHRP species eluted from the gel were assayed by the RIA of PTHRP1-34. PTHRP1-86 plasma concentrations by IRMA were less than 0.23 pmol/L in control subjects and patients with PH, and were significantly increased in patients with HHM (mean 6.1 pmol/L, P less than 0.001). In contrast, plasma PTHRP1-34 concentrations were not significantly different in the three groups; in HHM patients, the mean was 190 pmol/L. Plasma PTHRP37-67 concentrations were similar in control and PH groups and, although significantly increased in HHM patients (mean 440 pmol/L, P less than 0.002), showed poor diagnostic discrimination. PTHRP1-34 concentrations after affinity extraction of plasma were also significantly higher in HHM patients (mean 10.7 pmol/L, P less than 0.001), but showed incomplete diagnostic discrimination. We conclude that the diagnostic utility of the direct RIAs for quantifying PTHRP is markedly inferior to the IRMA of PTHRP1-86.
authors.affiliation: Wolfson Research Laboratories, Department of Clinical Chemistry, Queen Elizabeth Medical Centre, Birmingham, U.K.
authors.forename: W A
authors.initials: WA
authors.lastname: Ratcliffe
authors.forename: S
authors.initials: S
authors.lastname: Norbury
authors.forename: R A
authors.initials: RA
authors.lastname: Stott
authors.forename: D A
authors.initials: DA
authors.lastname: Heath
authors.forename: J G
authors.initials: JG
authors.lastname: Ratcliffe
mesh_terms: D006801:Humans; D006934:Hypercalcemia / Q000097:blood; D006961:Hyperparathyroidism / Q000097:blood*; D015592:Immunoradiometric Assay; D010281:Parathyroid Hormone / Q000097:blood*; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000097:blood*; D010455:Peptides / Q000097:blood*; D011506:Proteins; D011863:Radioimmunoassay
chemical_list: D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D010455:Peptides; D011506:Proteins; C068871:parathyroid hormone-related protein (1-86); C054296:parathyroid hormone-related protein (1-34)