Clinical and Laboratory Studies of a New ImmunoradiometricAssay of Parathyroid Hormone-Related Protein

Parathyroid hormone-related protein (PTHrP) was mea-sured in plasma by a new immunoradiometric assay (IRMA) from Nichols Institute. The assay is specific for PTHrP and shows excellent parallelism when measuring keratinocyte fluid, samples with high PTHrP content, and PTHrP-supplemented plasma. A precision profile estab-lished the assay detection limitat 0.7 pmol/L. PTHrP was unstable in plasma, but the degradation rate was patient-specific. Because delay in separation resulted in loss of PTHrP immunoreactivity, samples were collected into tubes containing protease inhibitors(aprotinin, leupeptin, pepstatin, and EDTA) and separated within 30 mm. Among normal subjects, 78 % had PTHrP values greater than the detection limit; the reference range established was <0.7-2.6 pmol/L. Of patients with hypercalcemi