PS-C21-9: REVISITING ORAL SALT LOADING TEST: A NEW CHEMILUMINESCENT IMMUNOASSAY OF 24-HOUR URINE ALDOSTERONE MEASUREMENT

Abstract

Primary aldosteronism (PA) is widely recognized as the most frequent cause of secondary hypertension, and its prevalence ranges from 5% to 10% in hypertensive patients. The number of patients diagnosed with PA has increased due to more frequent screening in JAPAN. PA is diagnosed by a screening test, followed by a confirmatory or exclusionary test and a subtype test using computed tomography and adrenal vein sampling. Measuring of the urinary aldosterone concentration is important in oral sodium loading test (OSLT), one of the confirmatory tests. Therefore, an accurate aldosterone measurement method is required for clinical practice. Since April 2021, the plasma aldosterone concentration has been measured by chemiluminescent enzyme immunoassay (CLEIA) in Japan. In the present study, we developed a new CLEIA using a two step sandwich method to measure the 24 hour urine aldosterone level. We collected urine samples and measured 24 hour urine aldosterone levels employing radioimmunoassay (RIA), CLEIA, and liquid chromatography tandem mass spectrometry (LC MS/MS). The results showed that the 24-hour urine aldosterone levels measured using CLEIA and LC MS/MS were significantly correlated. The 24 hour urine aldosterone levels measured using CLEIA and RIA were also significantly correlated. However, the aldosterone level measured by CLEIA was lower than that measured by RIA (slope, 0.729; intercept, 120.9). In Japan, a new guideline for primary aldosteronism has been announced, with changes in the aldosterone measurement method, and the cutoff values for oral sodium loading test (OSLT) were changed. Therefore, we examined the cut off value of the 24 hour urine aldosterone level after the OSLT. Receiver operating characteristic analysis revealed a cut off value for primary aldosteronism of 3 mcg/day.