Urinary 18-hydroxycortisol is superior to plasma 18-hydroxycortisol for primary aldosteronism subtyping

Urinary and plasma 18-hydroxycortisol (18-OHF) have been investigated for primary aldosteronism (PA) subtyping. However, there is no research exploring the impact of sample types on the diagnostic performance of 18-OHF in PA subtyping. In this study, 18-OHF levels in both urine and plasma were determined in patients with idiopathic adrenal hyperplasia (IHA), aldosterone-producing adenoma (APA), and essential hypertension (EH) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Urinary18-OHF was determined using an established LC-MS/MS method, whereas plasma18-OHF was measured by a modified LC-MS/MS method. Differences in urinary and plasma 18-OHF levels between APA, IHA, and EH patients were investigated by Kruskal-Wallis test for non-parametric analysis. The LC-MS/MS method yielded a lower limit of quantitation (LLOQ) of 18-OHF in urine of 4.28 nmol/L and 0.190 nmol/L in plasma. The intra- and inter-precision for urine and plasma methods were < 6%, with accuracies between 95.9% and 110.3%. Urinary and plasma 18-OHF in 12 IHA, 18 APA, and 91 EH patients were quantified and analyzed. Non-parametric analysis by Kruskal-Wallis test revealed that urinary 18-OHF levels in IHA and APA patients were significantly different (P  0.05), indicating that urinary 18-hydroxycortisol outperformed plasma 18-hydroxycortisol for primary aldosteronism subtyping.