• Zeng Guo, Marko Poglitsch, Brett C McWhinney, UngererJacobus P JJPJDepartment of Chemical Pathology, Pathology Queensland, Queensland Health, Brisbane, Queensland, Australia.Faculty of Medicine, University of Queensland, Brisbane, Queensland, Australia., Ashraf H Ahmed, Richard D Gordon, Martin Wolley, and Michael Stowasser.
• Endocrine Hypertension Research Centre, University of Queensland Diamantina Institute, Greenslopes and Princess Alexandra Hospitals, Brisbane, Queensland, Australia.
• Clin. Chem. 2020 Mar 1; 66 (3): 483-492.

BackgroundMany medications (including most antihypertensives) and physiological factors affect the aldosterone/renin ratio (ARR) when screening for primary aldosteronism (PA). We sought to validate a novel equilibrium angiotensin II (eqAngII) assay and compare correlations between the aldosterone/angiotensin II ratio (AA2R) and the current ARR under conditions affecting the renin-angiotensin system.MethodsAmong 78 patients recruited, PA was excluded in 22 and confirmed in 56 by fludrocortisone suppression testing (FST). Peripheral levels of eqAngII, plasma renin activity (PRA) and direct renin concentration (DRC) were measured.ResultsEqAngII showed good consistency with DRC and PRA independent of PA diagnosis, posture, and fludrocortisone administration. EqAngII showed close (P < 0.01) correlations with DRC (r = 0.691) and PRA (r = 0.754) during FST. DRC and PRA were below their assays' functional sensitivity in 43.9% and 15.1%, respectively, of the total 312 samples compared with only 7.4% for eqAngII (P < 0.01). Bland-Altman analysis revealed an overestimation of PRA and DRC compared with eqAngII in a subset of samples with low renin levels. The AA2R showed not only consistent changes with the ARR but also close (P < 0.01) correlations with the ARR, whether renin was measured by DRC (r = 0.878) or PRA (r = 0.880).ConclusionsDynamic changes of eqAngII and the AA2R show good consistency and close correlations with renin and the ARR. The eqAngII assay shows better sensitivity than DRC and PRA assays, especially at low concentrations. Whether the AA2R can reduce the impact of some factors that influence the diagnostic power of the ARR warrants further study.© American Association for Clinical Chemistry 2020. All rights reserved. For permissions, please email: journals.permissions@oup.com.

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