Screening for Primary Aldosteronism: Aldosterone to Renin Ratio (ARR) Using Two Automated Chemiluminescent Immunoassays

Presentation Number: SAT-0849
Date of Presentation: June 21st, 2014

Martin Bidlingmaier*1, Harald Schmidt2 and Christoph Milczynski2
1Klinikum der Universität München, München, Germany, 2Limbach Laboratory, Heidelberg, Germany

Abstract

Primary Aldosteronism (PA) is the most common form of secondary hypertension. Prevalence in patients with Resistant Hypertension (uncontrolled blood pressure despite ≥ 3 antihypertensive drugs) is estimated in prospective studies to be 14-23%. The Aldosterone to Renin Ratio (ARR) can be used in the screening and is recommended by clinical practice guidelines in patients at risk. Use of ARR depends on the availability of reliable and sensitive methods to measure Aldosterone and Renin. We investigated the performance of a new automated, commercially available Chemiluminescent Immunoassay (CLIAs) for measurement of Aldosterone in comparison to our standard Aldosterone assay (RIA) with clinical samples. Aldosterone (PAC) was measured using the new CLIA on the LIAISON Analyzer (DiaSorin, Saluggia, Italy) and the Siemens coat-a-count RIA. Direct Renin (DRC) was measured on the LIAISON Analyzer. EDTA plasma samples were taken from 200 normotensive patients (N), 50 essential hypertensive (EH) patients and 50 PA patients. The latter groups were defined by post-saline Aldosterone >50pg/mL (RIA). 50 matched serum/plasma samples were measured with the LIAISON Aldosterone CLIA to analyze matrix commutability. Median PAC by RIA were 58pg/mL (range 35-259pg/mL) in N; 60 pg/mL (range 35-181 pg/mL) in EH and 221pg/mL (45-761pg/mL) in PA. Median PAC by CLIA was 70pg/mL (range 30-228 pg/mL) in N; 81 pg/mL (range 30-193pg/mL) in EH and 234pg/mL (range 45–670pg/mL) in PA. DRC was 20µU/mL (range 3-274µU/mL) in N; 50µU/mL (range 5-625µU/mL) in EH and 7µU/mL (range 2-35µU/mL) in PA. ROC analysis of the data identified a range of ARR values between 9.5 to 12.0 (PAC pg/mL; DRC µU/L) that provide acceptable balance between sensitivity and specificity (100%/80% to 98%/86%). Passing Bablok comparison of aldosterone concentrations from CLIA versus RIA revealed good correlation and agreement (y=1.04x+4.28). Significant correlation was observed between serum and plasma samples using the CLIA (r2=0.92; y=0.987+8.2). Preliminary data from salt load suppression tests and the high correlation to aldosterone concentrations measured by RIA indicate that the cut-off value (50pg/mL) can be used also for aldosterone concentrations measured by CLIA. Our data indicate that the new automated aldosterone CLIA in conjunction with the established automated CLIA for renin concentration can be used as a reliable and sensitive method for definition of the ARR.

 

Disclosure: MB: Speaker, DiaSorin. Nothing to Disclose: HS, CM