Determination of serum aldosterone by liquid chromatography and tandem mass spectrometry: a liquid-liquid extraction method for the ABSCIEX API-5000 mass spectrometry system.

Aims: Accurate serum aldosterone determination is critical to the screening and diagnosis of primary aldosteronism, the localisation of aldosterone producing tumours, and the investigation of other disorders of the renin-angiotensin system. Mass spectrometry offers a means to overcome problems with method-dependent bias between competitive immunoassays for aldosterone. The authors have developed a simple, sensitive and precise liquid-liquid extraction aldosterone method for the ABSCIEX API-5000 liquid chromatography and tandem mass spectrometry (LC-MS/MS) system.

Methods: Using d7-aldosterone internal standard, 500 μl of sample is extracted with 2500 μl of methyl tertbutyl ether followed by dry-down, reconstitution and LC-MS/MS analysis in ESI negative mode. Method validation was undertaken using standard approaches and comparison made against a commercial radioimmunoassay. Accuracy was assessed using EQA material with assigned aldosterone concentrations.

Results: The assay was linear up to 3420 pmol/l (LOQ=50 pmol/l, LOD<22 pmol/l). Total CVs were ≤5% for concentrations ≥120 pmol/l and 10% at the LOQ. Mean accuracy was 98.5% against GCMS assigned material.

Conclusion: The authors present a precise, sensitive and simple aldosterone method suitable for routine clinical use that requires no solid phase extraction or specialised ion sources.