Combination of LC-MS/MS aldosterone and automated direct renin in screening for primary aldosteronism.

BACKGROUND: Aldosterone to renin ratio (ARR) is used in screening for primary aldosteronism (PA). However, there are only few studies on the influence of assay methods on ARR and its cut-off limits. METHODS: Plasma direct renin immunoreactivity by chemiluminescence immunoassay (DR) was compared to renin activity assay (PRA), and a specific liquid chromatography-mass spectrometric method (LC-MS/MS) to radioimmunoassay (RIA) for plasma aldosterone. There were 75 samples for renin assays, and 42 samples of 39 patients for both renin and aldosterone assays. PA screening was considered positive if ARR by the aldosterone RIA:PRA was ≥800pmol/L:µg/L/h or by LC-MS/MS:DR≥44pmol/L:ng/L. RESULTS: The correlation between the DR and PRA methods (n=75, r(2)=0.845) and between LC-MS/MS and RIA (n=42, r(2)=0.973) was high in general, but low between the renin methods (n=49, r(2)=0.435) at low PRA values. When ARR was used in screening for PA, there were three divergent cases (positive only by alternative methods), but when applied in combination with criteria for elevated aldosterone, the methods showed good agreement, resulting in eight positive and 31 negative screening results. CONCLUSIONS: The automated DR assay combined with LC-MS/MS method for aldosterone provides a rapid, reliable, and specific method for screening of PA.