Enhancement of specificity of aldosterone measurement in human serum and plasma using 2D-LC-MS/MS and comparison with commercial immunoassays.

Accurate measurement of aldosterone is important for the standardized testing of primary hyperaldosteronism. Commercial immunoassays show substantial between-method variations resulting in significant clinical consequences. We developed a specific two dimensional (2D)-LC-MS/MS method for measuring aldosterone in human serum and plasma and compared it with three commercial immunoassays and an LC-MS/MS method. 250 μL samples, controls and calibrators spiked with d4-aldosterone were subjected to liquid-liquid extraction. The samples were analyzed using negative mode electrospray and 2D-LC followed by MS detection using an ABSciex 5500 mass spectrometer and compared with immunoassays of Siemens (Coat-A-Count), DiaSorin (CLIA-LIAISON), and IBL (ELISA). Data was acquired using multiple reaction-monitoring mode. LOQ and LOD of the method were 0.04 and 0.02 nmol/L respectively. The assay was linear up to 166 nmol/L. Inter and intra-assay imprecision at 0.13, 1.38 and 8.30 nmol/L were <10%. Interferences were absent and no differences were observed between serum and plasma matrices. Method recovery ranged from 95% to 113%. Ion suppression was not observed. Evaluated immunoassays showed positive biases ranging between 22% and 37% when compared with the developed method. We developed and validated an accurate method for measurement of aldosterone in human serum and plasma using 2D-LC-MS/MS which is suitable for clinical purposes. The method is faster than previously published LC-MS/MS methods, uses less sample, has adequate sensitivity while being able to preserve high specificity in a cost effective manner. Linearity of the assay makes it promising for urine and adrenal venous samples. Comparison with three commercial immunoassays demonstrates the advantages of the developed method.