EVALUATION OF A NEW, RAPID AND AUTOMATED IMMUNOCHEMILUMINOMETRIC ASSAY FOR THE MEASUREMENT OF SERUM INTACT PARATHYROID-HORMONE

The Immulite parathyroid hormone (PTH) immunochemiluminometric assay ( ICMA) was evaluated by measuring serum PTH concentrations in 134 volun teers and 251 patients with various diseases affecting bone and minera l metabolism and comparing with those measured by the Nichols Allegro immunoradiometric (IRMA) assay. Although the assays were highly correl ated (r=0.99, P<0.0001), there were discrepancies at lower PTH concent rations which may be explained by the lower limit of detection of the ICMA assay. The anti-coagulants EDTA and heparin appeared to have sign ificant effects on PTH measurement particularly at lower concentration s. Sera assayed by ICMA diluted out more uniformly than in the IRMA an d there was no cross reactivity with parathyroid hormone-related pepti de in either the IRMA or ICMA. Delays of up to 8h in specimen handling did not appear to affect PTH measurements. The enhanced sensitivity o f the Immulite ICMA intact PTH assay confers an advantage in the diagn osis of both hyper- and hypocalcaemia, while the shorter incubation ti mes, automation and lack of radioactivity are important practical adva ntages.