Immunoreactivity of plasma parathyrin-related peptide: three region- specific radioimmunoassays and a two-site immunoradiometric assay compared

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 37; no. 10; pp. 1781 - 1787
• Main Authors: Ratcliffe, WA, Norbury, S, Stott, RA, Heath, DA, Ratcliffe, JG
• Format: Journal Article
• Language: English
• Published: Washington, DC Am Assoc Clin Chem 01.10.1991; American Association for Clinical Chemistry
• Subjects: Aminoacids, peptides. Hormones. Neuropeptides; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Humans; Hypercalcemia - blood; Hyperparathyroidism - blood; Immunoradiometric Assay; Parathyroid Hormone - blood; Parathyroid Hormone-Related Protein; Peptide Fragments - blood; Peptides - blood; Proteins; Radioimmunoassay; Human; Protein hormone; Biological fluid; Parathormone; Analog; Radioimmunoassay; Clinical biology; Tumoral marker; Comparative study; Quantitative analysis; Blood plasma
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/37.10.1781

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.