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O'Shea, PM,Griffin, TP,Browne, GA,Gallagher, N,Brady, JJ,Dennedy, MC,Bell, M,Wall, D,Fitzgibbon, M
Practical Laboratory Medicine
Screening for primary aldosteronism using the newly developed IDS-iSYS (R) automated assay system
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Primary aldosteronism Renin Aldosterone Aldosterone: renin ratio (ARR) Sensitivity Specificity
Background: The recommended approach to screening for primary aldosteronism (PA) in atrisk 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) cutoffs for PA in men and women using the IDS-iSYS (R) 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 (R) 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.
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