State of the art of aldosterone immunoassays. A multicenter collaborative study on the behalf of the Cardiovascular Biomarkers Study Group of the Italian Section of European Society of Ligand Assay (ELAS) and Società Italiana di Biochimica Clinica (SIBIOC).

Two new immunoassay methods for aldosterone assay using automated platforms recently became available into market. The main aim of the present study is to evaluate the analytical performance of these automated direct immunoassay methods, and also to compare their analytical characteristics to those of the most popular RIA and EIA methods used in an Italian External Quality Assessment (EQA) study. In this study analytical performances of two aldosterone immunoassays using the IDS iSYS and DiaSorin LIAISON fully automated platforms, were evaluated. Results obtained with the two platforms in EDTA plasma samples of healthy subjects and patients were compared with those obtained by RIA and EIA methods used in the Italian EQA scheme, named Immunocheck study. The two automated methods showed similar analytical performances: LoD 83.9 vs 92.2 pmol/L, LoQ 104.4 vs 111.1 pmol/L, respectively; moreover, the within-run and total imprecision values showed CV% between 8.1 and 14.1 for samples with 180.8 and 387.2 pmol/L concentration for both methods. There was a close linear regression between methods, however we found a significant proportional bias between LIAISON and iSYS methods. The EQA samples results obtained with these two methods were highly correlated to the consensus mean values. Our data indicate that aldosterone values measured with the two automated methods actually show better reproducibility, shorter laboratory Turn Around Time (TAT) and require less "hands on labor" compared to RIA and EIA immunoassays. However, in our study significant bias was observed in result comparison, this means that translating aldosterone concentration in clinical information an appropriate definition of reference ranges for each method is mandatory.