Primary aldosteronism (PA) is the most common cause of secondary hypertension. Liquid chromatography - tandem mass spectrometry (LC-MS/MS) is more accurate than the traditional radioimmunoassay in measuring aldosterone. This study aims to establish a more precise diagnostic threshold for the oral sodium loading test (OSLT) by using LC-MS/MS to measure urinary aldosterone levels. We will combine the biochemical results of OSLT and other data from healthy volunteers and suspected PA patients to determine a new 24-hour urinary aldosterone threshold. We expect to improve the diagnostic accuracy of PA, helping clinicians identify this curable cause of hypertension earlier and more accurately, and achieving precise treatment.