Unquantifiably low aldosterone concentrations are prevalent in hospitalised COVID-19 patients but may not be revealed by chemiluminescent immunoassay

Objective Previous studies have reported conflicting findings regarding aldosterone levels in patients hospitalised with COVID-19. We therefore used the gold-standard technique of liquid chromatography tandem mass-spectrometry (LCMSMS) to address this uncertainty. Design All patients admitted to Cambridge University Hospitals with COVID-19 between March 10, 2020 and May 13, 2021, and in whom a stored blood sample was available for analysis, were eligible for inclusion. Methods Aldosterone was measured by LCMSMS and by immunoassay; cortisol and renin were determined by immunoassay. Results Using LCMSMS, aldosterone was below the limit of detection (<70 pmol/L) in 74 (58.7%) patients. Importantly, this finding was discordant with results obtained using a commonly employed clinical immunoassay (Liaison Diasorin®), which over-estimated aldosterone compared to the LCMSMS assay (intercept 14.1 [95% CI -34.4 to 54.1] + slope 3.16 [95% CI 2.09 to 4.15] pmol/L). The magnitude of this discrepancy did not clearly correlate with markers of kidney or liver function. Solvent extraction prior to immunoassay improved the agreement between methods (intercept -14.9 [95% CI -31.9 to -4.3] and slope 1.0 [95% CI 0.89 to 1.02] pmol/L) suggesting the presence of a water-soluble metabolite causing interference in the direct immunoassay. We also replicated a previous finding that blood cortisol concentrations were often increased, with increased mortality in the group with serum cortisol levels >744 nmol/L (p=0.005). Conclusion When measured by LCMSMS, aldosterone was found to be profoundly low in a significant proportion of patients with COVID-19 at the time of hospital admission. This has likely not been detected previously due to high levels of interference with immunoassays in patients with COVID-19, and this merits further prospective investigation.