Indapamide interference in liquid chromatography-tandem mass spectrometry aldosterone assay

The aldosterone renin ratio (ARR) is used as a screening test for primary aldosteronism (PA), and this requires measurement of both aldosterone and renin. Aldosterone is usually measured using immunoassay or liquid chromatography-mass spectrometry techniques. Antihypertensive medications should be discontinued prior to screening as they can interfere with interpretation of results. Indapamide is a thiazide-like diuretic commonly used in the treatment of hypertension. NICE guidance (NG136 2019) recommends the use of indapamide over more conventional thiazide diuretics. Indapamide has been noted to cause interference in a liquid chromatography-mass spectrometry method by interfering in the measurement of aldosterone-d4 internal standard. This leads to falsely increased concentrations of aldosterone which can lead to unnecessary further investigations.