Screening for primary aldosteronism using the newly developed IDS-iSYS® automated assay system

• Main Authors: P.M. O’Shea, T.P. Griffin, G.A. Browne, N. Gallagher, J.J. Brady, M.C. Dennedy, M. Bell, D. Wall, M. Fitzgibbon
• Format: Article
• Language: English
• Published: Elsevier 2017-04-01
• Series: Practical Laboratory Medicine
• Online Access: http://www.sciencedirect.com/science/article/pii/S2352551716300464

Background: The recommended approach to screening for primary aldosteronism (PA) in at-risk populations is to determine the ratio of aldosterone concentration (serum (SAC)/plasma (PAC)) to renin measured in plasma as activity (PRA) or concentration (DRC). However, lack of assay standardisation mandates the need for method-specific decision thresholds and clinical validation in the local population. Aim: The study objective was to establish method-specific aldosterone: renin ratio (ARR) cut-offs for PA in men and women using the IDS-iSYS® assay system (IDS plc). Methods: A prospective cohort study design was used. PAC and DRC were measured immunochemically in ethylenediamine-tetraacetic acid (EDTA) plasma on the IDS-iSYS® instrument. Results: A total of 437 subjects (218 men, 219 women) were recruited including: healthy normotensive volunteers (n=266) and women taking the oral contraceptive pill (OCP; n=15); patients with essential hypertension (EH; n=128); confirmed PA (n=16); adrenal cortical carcinoma (ACC; n=3); Addison's disease (AD; n=4) and phaeochromocytoma/paraganglioma (PPGL; n=5). In this population, an ARR cut-off at>37.4 pmol/mIU provided 100% diagnostic sensitivity, 96% specificity and positive likelihood ratio for PA of 23:1. When the ARR decision threshold was stratified according to gender, a cut-off of>26.1 pmol/mIU in men and>113.6 pmol/mIU in women resulted in diagnostic sensitivity and specificity of 100%. Conclusion: This study demonstrates that decision thresholds for PA should not only be method-specific but also gender-specific. However, given the small number of PA patients (n=16), particularly women (n=4), further validation through a prospective study with a larger PA cohort is required before the thresholds presented here could be recommended for routine clinical use. Keywords: Primary aldosteronism, Renin, Aldosterone, Aldosterone: renin ratio (ARR), Sensitivity, Specificity