Comparison of two immunoradiometric assays for parathyroid hormone-relatedprotein in the evaluation of cancer patients with and without hypercalcemia

Hypercalcemia is a common paraneoplastic syndrome due to the secretion by t umors of parathyroid hormone-related protein (PTHrP) and/or other osteolyti c factors. In the present study, we have measured plasma PTHrP using two im munoradiometric assays for PTHrP, assay N (Nichols) and assay I (INCSTAR), recognizing the 1-86 domain of PTHrP, for the evaluation of malignancy-asso ciated hypercalcemia. The study included 25 tumor patients with hypercalcem ia (HCa) [corrected serum calcium (SCa) greater than or equal to 2.70 mmol/ L], 20 normocalcemic patients with cancer (NCa), and ten healthy control su bjects. Plasma PTHhP was either undetectable or within the respective norma l range in the majority of NCa patients and in the control subjects, with b oth assays. Plasma PTHrP was increased in 13 and 15 of HCa cases with assay N and assay I, respectively. PTHrP was elevated in plasma in 5/6 (assay N) and 3/6 (assay I) HCa patients with squamous tumors. However, plasma PTHrP was high in only 2/9 (assay N) and 1/9 (assay I) HCa cases with hematologi cal tumors. Less than 40% of HCa patients with bone metastases, and >75% of those without bone involvement, had elevated plasma PTHrP with both assays . Detectable plasma PTHrP and SCa were significantly correlated using assay N (p = 0.025) and assay I (p = 0.01), in the HCa group. A highly significa nt correlation (p < 0.001) was found between detectable plasma PTHrP with b oth assays; and a high agreement between them based on simple kappa statist ics (p < 0.001), in the latter group. Our results indicate that each assay may be similarly useful in detecting PTHrP hyperproduction in cancer patien ts. (C) 1998 Elsevier Science B.V. All rights reserved.