A1728 Measurement of aldosterone

Abstract

Objectives: To compare aldosterone assay by RIA with LC-MS/MS and to evaluate the performance of proposed LC-MS/MS-specific cut-offs for primary aldosteronism (PA) screening and confirmatory testing. Methods: Peripheral aldosterone concentration (PAC) was tested by both methods among 52 patients during fludrocortisone suppression testing (FST). Direct renin concentration (DRC) was measured by CLIA. The proposed PACLC-MS/MS cut-offs for the aldosterone/renin ratio (ARR) and FST were derived from the regression equation obtained from our previous in-house comparison between two assays. Results: The obtained equation was PACLC-MS/MS = 0.79 × PACRIA-28.1 (R2 = 0.87, n = 200). In this study, median PACLC-MS/MS was 29.3% lower (p < 0.05) than PACRIA. A positive correlation (Spearman coefficient 0.92, p < 0.01) and linear relationship (p < 0.01, R2 = 0.81, n = 208) were observed between the two assays, with a positive bias of 34.5% (95% limits of agreement: −34.2% to 103.3%) for RIA. Forty-one patients showed conclusive FSTs (37 consistent and 4 inconsistent by two assays) A good agreement (Kappa coefficient 0.74, p < 0.01) and no differences were observed between the current FST day 4 upright PACRIA cut-off of 165 pmol/L and the proposed PACLC-MS/MS cut-off of 130 pmol/L. Among the 37 patients with consistent FSTs, no differences were observed in sensitivity (89.7% vs 93.1%) and specificity (87.5% for both) between the current ARRRIA cut-off of 70 and the proposed ARRLC-MS/MS cut-off of 55. Conclusion: Adjustment of the current cut-off for PA diagnostic testing is necessary if PACLC-MS/MS is measured. Our preliminary results revealed that the proposed cut-offs of 55 for the ARR (PACLC-MS/MS/DRC) and 130 pmol/L for FST day 4 upright PACLC-MS/MS perform as well as the current RIA threshold values.