[Performances of two kits for parathyroid hormone-related peptide (PTHrP) assay in the additional study of malignant hypercalcemias].

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 remains difficult. After a study evaluating the methodological reliability, we measured the contribution of PTHrP to the hypercalcemia by 2 assays: a N-terminal RIA and a 1-72 IRMA in samples from 47 control subjects, 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 hypercalcemia. We noted a strong correlation (r = 0.92) between the two assays. They do not show increases in renal insufficiency; they have a good diagnostic discrimination between HPT, normal subjects and patients with MHH. Elevated levels of PTHrP are similar in both assays. However, IRMA appears to be more sensitive and more practical than RIA. Moreover, it shows the best correlation between serum calcium and phosphorus in patients with MHH.