Endocrine Abstracts

Background: Screening for primary aldosteronism (PA) using the aldosterone to renin ratio (ARR) is recommended by clinical practice guidelines in patient groups with a high prevalence as the disease is reported by several authors in more than 10% of essential hypertensives (EH).

Methods: Plasma aldosterone concentration (PAC) and direct renin (DR) were measured using two novel automated chemiluminescence assays (IDS-iSYS; Boldon, UK) and compared to the Siemens RIA and Diasorin Liaison (LSN) respectively. Plasma was taken from 20 controls, 26 EH and 36 PA patients. PA was defined by lack of aldosterone salt-load suppression to <50 pg/ml. Mineralocorticoid receptor antagonists and b-blockers were excluded, other medication was not restricted. Hypokalemia was controlled in all. Using Siemens PAC (pg/ml)/Liaison DR (mU/l), our laboratory cut-off for diagnosis of PA is 12.

Results: PACs in controls, EHs and PAs were (mean; 25–75%ile) RIA: 157 (84.2–196), 123 (73.3–137), and 274 (190–320) pg/ml and iSYS: 115 (50.5–182), 114 (68.7–131), and 279 (172–348) pg/ml. In the same groups DR using the LSN assay was at 33 (21.2–43.1), 62 (8.9–82.2), and 7.9 (2.0–9.5), and with the iSYS 40.1 (27.4–47.8), 77.9 (13.6–110), and 14.1(4.9–13.7). Using linear regression analysis aldosterone-iSYS=1.073RIA±0.082, r²=0.69 and renin-iSYS=1.057LSN±0.067, r²=0.77. Using a diagnostic cut-off of 12 with the RIA and LSN, ROC curve analysis of this cohort gives a sensitivity of 96.7% and specificity of 85.1%. As at this cut-off the iSYS assays provide 93.6% sensitivity, a lower cut-off at 6.3 would provide corresponding 96.7% sensitivity with 84.8% specificity.

Conclusions: The data presented here show good correlation between commonly used aldosterone and renin assays and the newly automated IDS-iSYS system. An overall trend for higher renin values using the iSYS, albeit with equivalent discrimination between the three cohort groups, would require a lower ARR cut-off to provide the same diagnostic power.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.