Validation and clinical evaluation of diagnostic ability of novel chemiluminescent enzyme immunoassay of plasma aldosterone concentration.

Plasma aldosterone concentration has been usually measured by radioimmunoassay and chemiluminescent enzyme immunoassay which have demonstrated lack of high specificity and variability in assay performances. Liquid chromatography-tandem mass spectrometry is considered to be ideal measurement method of plasma aldosterone, however it takes relatively high cost and measurement time. We recently developed a novel non-competitive chemiluminescent enzyme immunoassay for plasma aldosterone concentrations by the fully automated assay system. We performed clinical validation of diagnostic ability of the new assay-based screening of 344 hypertensive patients including 133 patients with primary aldosterone producing adenoma, 100 patients with bilateral hyperaldosteronism, and 111 patients with essential hypertension. Passing-bablok analysis revealed that the new measurement of plasma aldosterone concentration was significantly correlated and almost equivalent to liquid chromatography-tandem mass spectrometry measurement of aldosterone; the regression slope and intercept were 0.962 and -0.043, and the correlation coefficient was 0.962, which is more similar than radioimmunoassay especially in lower range (< 10 ng/dL). Bland-Altman plot analysis with the mass-spectrometry measurement also demonstrated that both bias and limits of agreement with 95% confidence interval of the automated aldosterone assay were smaller than those of the radioimmunoassay, suggesting smaller systemic errors in the novel measurement. The lowest plasma aldosterone concentration and ratio of aldosterone-over-renin concentrations in aldosterone producing adenoma group were 6.0 ng/dL and 16.3 ng/dL per pg/mL/hr, respectively. We suggest if aldosterone-over-renin concentrations is over 15 ng/dL per pg/mL/hr, the patient should be performed confirmatory test for primary aldosteronism. The novel chemiluminescent enzyme immunoassay is clinically reliable alternative for conventional radioimmunoassay and liquid chromatography-tandem mass spectrometry to provide better throughput and cost-effectiveness in diagnosis of primary aldosteronism from larger number of hypertensive patients.