Macro-aldosterone as a false positive screening for primary aldosteronism

Abstract

Macro-hormones are hormone-immunoglobulin complexes that lack bioactivity. They are considered immunoassay artifacts, as these techniques cannot distinguish them from the monomeric bioactive molecule, therefore resulting in higher hormone levels detected. This situation has been commonly described for the case of peptide hormones but not for steroids. We report the case of a 46-year-old woman with hypertension and left ventricular hypertrophy who was assessed for primary aldosteronism (PA) showing plasma aldosterone levels over the detection limit and a very suggestive aldosterone-to-renin ratio. Confirmatory testing with oral sodium overload discarded PA and exposed discordant plasma versus urine aldosterone measurements. Re-testing hormone after plasma sample pre-treatment with polyethylene glycol (PEG) for large protein precipitation, resulted in normal aldosterone levels, thus demonstrating the existence of macro-aldosterone complexes. Although liquid chromatography with tandem mass spectrometry is a gold standard method for steroidal hormones analysis, it is still unavailable in many clinical laboratories. PEG pre-treatment is a simple, quick and unexpensive technique that allows more accurate measurements by immunoassays when macro-hormones complexes are present in plasma.