Evaluation of a chemiluminescent immunoassay for urinary aldosterone on the DiaSorin LIAISON automated platform against RIA and LC-MS/MS

Urinary aldosterone quantitation has an important but small role to play in the investigation of primary aldosteronism (PA) and less commonly, for secondary aldosteronism and hypoaldosteronism. It is most often used following the oral sodium loading challenge as a confirmatory test for diagnosis of PA [1]. Until recently, most laboratories were offering radioimmunoassay (RIA) detection of urinary aldosterone. A smaller number of laboratories have developed liquid chromatography-tandem mass spectrometry (LC-MS/ MS) methods which are expected to be superior to immunoassays from the perspective of analytical specificity. Two automated competitive chemiluminescent immunoassays (CLIA) for the quantitative determination of aldosterone in plasma, serum, and urine samples have become available. The CLIA assays can potentially improve turn-around time and reliability for urinary aldosterone measurement without the use of radiotracers. For the LIAISON assay (Diasorin, Saluggia, Italy), sample preparation requires acid hydrolysis for conversion of metabolites such as aldosterone-18-oxo-glucuronide to aldosterone. While this sample-preparation procedure is manual, the remainder of the procedure is automated, reducing the number of steps compared to RIA. Here, we describe the analytical evaluation for the urinary aldosterone method on the DiaSorin-LIAISON platform and provide patient comparison data to conventional RIA and LC-MS/MS methods. Urine samples were subject to acid hydrolysis (one part urine and two parts 0.2 N HCl) for 18 h at 30 °C. After acid hydrolysis, the samples were neutralized by mixing one part urine with four parts of LIAISON aldosterone neutralization buffer. Hydrolyzed samples were measured using the DiaSorin LIAISON analyzer, which is a two-step competitive chemiluminescent assay. Linearity was assessed using six admixtures of a high patient pool at a concentration near the upper end of the analytical measuring range with a low patient pool. Each mixed sample was measured in duplicate. The assay demonstrated a wide linear range from 4.5 to 36.4 nmol/L (least squares regression y = 1.02x − 0.16). The imprecision for twice-daily measurements over a 10-day period was evaluated for both process and assay controls. For process controls which included acid hydrolysis and neutralization steps prior to measurement on the LIAISON instrument, total imprecision was low across different concentration ranges. Coefficient of variation (CV) values were 7.07% at 3.14 nmol/L, 6.80% at 9.89 nmol/L for Bio-Rad QC materials (Lyphochek® Quantitative Urine QC, Bio-Rad, Hercules, CA, USA), and 2.83%, 4.77% and 3.42% for patient pools at 6.15, 14.49, and 26.55 nmol/L, respectively (Table 1). aPresent address: Division of Biochemistry, Department of Pathology and Laboratory Medicine, The Ottawa Hospital, Ottawa, Ontario, Canada. bPresent address: Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada. *Corresponding author: Paul M. Yip, Department of Clinical Biochemistry, University Health Network, 200 Elizabeth Street, 3 EB 362, Toronto, ON M5G 2C4, Canada, Phone: +1-416-340-3551, E-mail: paul.yip@utoronto.ca; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada; and Laboratory Medicine Program, University Health Network, Toronto, ON, Canada Dan C. Lin and Joshua E. Raizman: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada Daniel T. Holmes: St. Paul’s Hospital, Department of Pathology and Laboratory Medicine, Vancouver, BC, Canada; and Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada Andrew C. Don-Wauchope: Hamilton Regional Laboratory Medicine Program, Hamilton, ON, Canada; and Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada