Background and Aims The saline infusion test (SIT) is a confirmatory test for the diagnosis of primary aldosteronism (PA). The diagnosis thresholds differ dependent on whether Plasma aldosterone concentration (PAC) was measured by immunoassay (IA) or liquid chromatography mass spectrometry (LCMS). For site who measure PAC on both systems, high prevalence of discordant SIT results has been described. This study aims to characterise the subsequent outcomes of patients with discordant SIT.
Methods This retrospective study evaluated 78 SITs, performed at a tertiary hospital in Australia. Clinical and biochemical differences between individuals with discordant and concordant SITs were analysed using Wilcoxon signed-rank tests and Pearson's Chi-squared tests. Correlation between IA and LCMS measurements was assessed by Pearson correlation coefficient.
ResultsĀ Discordance between IA and LCMS was observed in 48% of SITs. Patients with discordant results were more likely to be female (75% vs 37%, p=0.008), and normokalaemic without potassium supplement (50% vs 17%, p=0.019), compared to those with concordant abnormal results. Treated systolic blood pressure readings were not different (median 145 vs 159 mmHg, p=0.07). Biochemically, they had lower baseline and post-saline PAC, measured by IA and LCMS. Unilateral PA was less common in the discordant group (20% vs 69%, p=0.06). One patient with discordant SIT, who lateralised on adrenal venous sampling, achieved surgical cure post adrenalectomy.
Conclusions Individuals with discordant SITs exhibit a milder phenotype of PA. Given the potential for a surgical cure, AVS should still be considered.