OBJECTIVE: Subtyping of primary aldosteronism usually requires adrenal vein sampling (AVS). Interpretation can be compromised by apparent bilateral aldosterone suppression (ABAS), which we hypothesised reflects an artefact of the Liaison immunoassay of aldosterone. We therefore compared measurements of aldosterone by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with those by Liaison and iSYS immunoassays.

DESIGN: Observational multicentre study.

PATIENTS: The study involved 216 patients who underwent bilaterally selective non-stimulated AVS.

MEASUREMENTS: Adrenal and peripheral venous plasma aldosterone concentrations were measured by Liaison and iSYS immunoassays in 110 and 106 respective samplings compared to LC-MS/MS in all. Ratios of aldosterone-to-cortisol below 1.0 in adrenal versus peripheral vein samples defined relative aldosterone suppression.

RESULTS: Among all AVS procedures, 9.7% (21/216) of samplings with immunoassay measurements showed ABAS, threefold more (p = 0.0004) than the 3.2% (7/216) with LC-MS/MS. Rates of ABAS were particularly high with the Liaison immunoassay compared to LC-MS/MS (14.5% vs. 0.9%, p < 0.0001) and remained higher after substitution of immunoassay-measured with LC-MS/MS-measured cortisol (10.9% vs. 0.9%, p = 0.0007). Among 106 procedures involving iSYS immunoassay measurements, rates of ABAS at 4.7% were a third (p = 0.0202) those of the Liaison immunoassay and did not differ from LC-MS/MS measurements (5.7%). ABAS confined to LC-MS/MS measurements in one patient was resolved by a second sampling that revealed pronounced aldosterone secretion versus earlier suppression.

CONCLUSION: ABAS is a relatively common artefact of the Liaison immunoassay of aldosterone. More rarely, ABAS may reflect sampling blood from an adrenal venous tributary that does not drain from the site of excess aldosterone secretion.