Endocrine Abstracts (2008) 16 P49

Evaluation of aldosterone to renin concentration ratio as a reliable screening parameter for primary aldosteronism applying currently available assays

Nicole Unger1, Timo Deutschbein1, Martina Bröcker-Preuss2, Bianca Ueberberg1, Jakob Hinrichs3, Martin K Walz3, Kurt W Schmid4, Klaus Mann1 & Stephan Petersenn1

1Division of Endocrinology, University of Duisburg-Essen, Essen, Germany; 2Department of Clinical Chemistry and Laboratory Medicine, University of Duisburg-Essen, Essen, Germany; 3Department of Surgery and Centre of Minimally Invasive Surgery, Kliniken Essen-Mitte, Essen, Germany; 4Institute of Pathology and Neuropathology, University of Duisburg-Essen, Essen, Germany.

Plasma aldosterone concentration (PAC) to active renin concentration (ARC) ratio (ARR) is an established screening tool for primary aldosteronism. Previously we provided reliable cut-offs measuring PAC by a radioimmunoassay (RIA; Byk&DiaSorin) und ARC by an established immunoluminometric assay (Nichols Institute Diagnostics). Since the latter one is not longer available, we aimed to establish cut-offs for currently available assays.

One hundred seven subjects were studied, including 20 patients with primary aldosteronism (13 adrenal adenomas, 7 adrenal hyperplasia), 15 cortisol-producing adrenal adenomas, 14 pheochromocytomas, 16 nonfunctioning adrenal adenomas, 14 patients with essential hypertension and 34 normotensive volunteers. Patients were on various medications except for aldosterone antagonists. PAC was measured by RIA (Siemens AG), while ARC was determined by an automated chemiluminescent immunometric assay (Liaison, DiaSorin). Putative ratio thresholds were determined by ROC analysis. In 29 subjects, PAC und ARC determined by the current assays were correlated to values obtained by the Byk&DiaSorin/Nichols assay model.

ARR was significantly higher in patients with primary aldosteronism than in the control groups (P<0.0001). ROC analysis suggested an ARR threshold of 14.3 (sensitivity 90.0%, specificity 83.9%, AUC=0.9144). Additional consideration of PAC >130 ng/l demonstrated a lower sensitivity (80.0%) with higher specificity (95.7%). PAC measured by Siemens was lower (0.32×X+34 ng/l) compared to Byk&DiaSorin, and ARC measured by DiaSorin was higher (0.96×X+5 ng/l) compared to Nichols. Therefore, the current cut-off for ARR is much lower than the previously ones established.

An ARR of >14.3 is a reliable screening tool for primary aldosteronism under random conditions. Application of this assay-specific cut-off will clearly change the diagnosis in a relevant number of patients, compared to previously established ratios.