Background & Aim: Diagnosis of primary aldosteronism (PA) in current practice involves initial screening by plasma aldosterone-renin ratio (ARR) followed by confirmatory testing such as seated saline suppression test (SSST). Measurement of 24-hour urinary aldosterone concentration (24hr-UAC) collected after adequate sodium intake has been suggested as a potential test for diagnosis of PA, but its diagnostic performance/utility has not been well established. The aim of this study was to determine the diagnostic performance of 24hr-UAC analysed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for diagnosis of PA.
Methods: This is a retrospective data analysis of 24hr-UAC measured by LC-MS/MS and 24-hour urinary sodium concentration (24hr-UNa) (total n=182) collected prospectively from 177 patients who had SSST performed due to elevated ARR and/or to assess for biochemical cure post adrenalectomy for unilateral PA (n=14 out of 177) at the Princess Alexandra Hospital between August 2018 and July 2023. All tests were performed without interfering medications. Receiver operating characteristic curve (ROC) analyses were performed to assess the performance of 24hr-UAC at various 24hr-UNa for diagnosis of PA using the SSST as the gold standard reference test.
Results: One-hundred and twenty-seven (127) out of 182 were diagnosed as PA by positive SSST and 55 of 182 had negative SSST. Mean±SD 24hr-UAC were 50.6±3.2 nmol/24h in cases with positive SSST and 20.8±1.9 nmol/24h in those with negative SSST. ROC analysis revealed that 24hr-UAC ≥23.5 nmol/24h had 92.1% sensitivity and 82.6% specificity to identify PA in cases with 24hr-UNa ≥190 mmol/24hr (n=52; area under the curve=0.946). A higher cut-off 24hr-UAC ≥27.5 nmol/24h provided a higher specificity (92.3%) with 78.9% sensitivity.
Conclusion: 24hr-UAC analysed by LC-MS/MS in the setting of 24hr-UNa ≥190 mmol/24h can identify PA cases with high sensitivity and specificity.