DEVELOPING A MOST EQUIVALENT ALDOSTERONE MEASUREMENT TO LC-MS/MS BY A NOVEL HIGH-QUANTITATIVE NONCOMPETITIVE CHEMILUMINESCENCE IMMUNOASSAY

Abstract

Objective: Measurement of plasma aldosterone and renin concentration, or activity, is useful for selecting antihypertensive agents and detecting hyperaldosteronism in hypertensive patients. However, it takes several days to get results even if measured by inaccurate radioimmunoassay, or we must accept high-cost LC/MS, and development of a more rapid and accurate substitute has been long hoped. We have developed a novel, fully-automated, high-quantitative noncompetitive chemiluminescence immunoassay (NC-CLEIA) for detecting aldosterone in serum and plasma, and its performance is evaluated as compared to LC/MS measurement. Design and method: Recently a unique anti-metatype antibody, which recognizes the immunocomplex of aldosterone and its monoclonal antibody, was established. Using this antibody for sensing permitted the construction of non-competitive assay for the detection of aldosterone. The reaction protocol of novel aldosterone assay is the following. In the 1st reaction, aldosterone in patient's sample is captured on anti-body coated magnetic particles. Alkaline phosphatase-conjugated anti-metatype antibody is added and incubated as 2nd reaction following a wash. Then substrate solution is added after washing immunocomplex. The resulting reaction signals are proportional to the amount of aldosterone in the sample allowing quantitative determination of in serum or plasma sample. The overall reaction is completed within 30 min. Results: Limit of blank (LoB), limit of detection (LoD) and limit of quantitation (LoQ) of our NC-CLEIA aldosterone assay were 0.09 ng/dL, 0.21 ng/dL and 0.57 ng/dL, respectively. NC-CLEIA aldosterone measurements were linearly well correlated with LC/MS aldosterone measurements (N = 130, y = 1.027x - 0.23 ng/dL, Spearman's p = 0.996, p < 0.0001). Bland-Altman plot analysis between NC-CLEIA and LC-MS/MS of aldosterone revealed a bias of 0.40 ng/dL with the limits of agreement of -4.60 and 5.41 ng/dL with 95% confidence interval. Conclusions: Our novel NC-CLEIA aldosterone assay was well-correlated and had only a very low bias with LC-MS/MS method and also was able to accurately quantify low level samples even in essential hypertension patients. This assay may be useful for the routine analysis of aldosterone and for the screening and diagnosis of PA from large number of hypertensive patients.