Measurement of serum aldosterone in picomolar level by LC-MS/MS using charge-tagged technique

Aldosterone is a mineralocorticoid steroid hormone, the measurement of which in the clinical laboratory is principally performed for the investigation of primary hyperaldosteronism. Primary hyperaldosteronism is a specifically treatable and potentially curable form of hypertension, which typically presents as drug-resistant hypertension and, in up to 37% of cases, hypokalemia. Accurate measurement of aldosterone concentration is essential for correct diagnosis. The serum concentrations of aldosterone are in the picomolar range and therefore sensitive aldosterone assays are required. With the advancement in instrumentation of LC-MS/MS, the picomolar range of aldosterone can be easily measured by the newer models, but for those with a less sensitive instrument, special technique for sample preparation to enhance assay sensitivity is required. This work described the use of charge-tagging for the picomolar measurement of serum aldosterone in a less sensitive LC-MS/MS instrument. The assay was linear up to 3000 pmol/L with lower limit of quantitation at 80 pmol/L. The mean relative recovery was 96.5% with a range of 89.3-101.6% for aqueous calibrators and the mean relative recovery was 94.8% with a range of 87.5-101.4% for serum calibrators. Intra-assay CVs range from 8.2% to 11.3%, and inter-assay CVs ranged from 8.5% to 13.5% at concentration range from 229 to 1720 pmol/L. The LC-MS/MS method compared well (y = 1.04x + 8.97) with the in-use radioimmunoassay method. There was no significant difference found (p = 0.7135) between results determined by LC-MS/MS and radioimmunoassay method.