PERFORMANCES OF 2 ASSAYS OF PARATHORMONE- RELATED PEPTIDE (PTHRP) IN THE ADDITIONAL INVESTIGATION OF MALIGNANT HYPERCALCEMIA

Measurement of parathyroid hormone-related peptide (PTHrP) associated with that of parathyroid hormone, allows to establish, in most cases, diagnosis of hypercalcemia of malignancy and more exactly of patients with Malignancy Humoral Hypercalcemia (MHH). Because of the variety of molecular forms of PTHrP, linked to its catabolism, its immunoassay r emains difficult. After a study evaluating the methodological reliabil ity, we measured the contribution of PTHrP to the hypercalcemia by 2 a ssays : a N-terminal RIA and a 1-72 IRMA in samples from 47 control su bjects, 10 patients with chronic renal failure (IRC), 13 patients with primary hyperparathyroidism (HPT), and 48 patients with solid tumors classified by their level of calcemia: 48 normocalcemia and 23 hyperca lcemia. We noted a strong correlation (r = 0,92) between the two assay s. They do not show increases in renal insufficiency; they have a good diagnostic discrimination between HPT, normal subjects and patients w ith MHH. Elevated levels of PTHrP are similar in both assays. Howewer, IRMA appears to be more sensitive and more practical than RIA. Moreov er, it shows the best correlation between serum calcium and phosporus in patients with MHH.