Evaluation of a chemiluminescence immunoassay for the determination of intact parathyroid hormone using the ADVIA Centaur

Abstract

We tested a new chemiluminescence immunoassay for intact parathyroid hormone (PTH) (ADVIA Centaur intact PTH-serum assay). It is a two-site sandwich immunoassay using direct chemiluminescence technology. We investigated precision with serum pools at three levels of the analyte, analyzed in duplicate for 12 days. Total coefficients of variation (CVs) were between 4.6 and 14.4%. The intra-assay precision was between 4.4 and 6.1%. Day-to-day reproducibility was between 1.5 and 13.1% for pools with a PTH concentration between 10 pg/ml and 70 pg/ml (about 1 to 7 pmol/l). The analytical sensitivity was 3.1 pg/ml. The functional sensitivity did not differ from 3 SD minimal detectable concentration (MDC). The linearity was good in the range from 3.1-1930 pg/ml. Comparison with the IRMA used in our laboratory was analyzed by Passing-Bablok and Bland-Altman plots and revealed a proportional bias of +/-60% (slope: 1.58; IC: 1.53 to 1.63) and a systematic bias of -3.3 pg/ml which should not have any clinical consequence in the interpretation of the results. We established a reference range based on our hospital population. We evaluated 87 subjects without abnormality of calcium metabolism and with normal vitamin D supply. Three groups of patients were also analyzed: 57 patients with vitamin D insufficiency, 17 with renal failure and 15 with hypercalcemia (7 due to primary hyperparathyroidism and 8 due to another etiology). Reference ranges were from 10.2 to 93 pg/ml for CLIA measurement and from 6.4 to 68 pg/ml for IRMA measurement. PTH values measured by CLIA varied from 6 to 142 pg/ml in patients with vitamin D insufficiency. By CLIA measurement, intact PTH was between 26 and 892 pg/ml in renal failure, between 54 and 201 pg/ml in primary hyperparathyroidism and between 0 and 29 pg/ml in patients with another etiology of hypercalcemia. The results of PTH measurements in EDTA plasma did not differ significantly from those performed in serum (Passing Bablock).