SAT-064 Validation of Furosemide Upright Test in Primary Aldosteronism Diagnosis Using Direct Renin Assay

Primary aldosteronism (PA) is the most common cause of endocrine hypertension. The 2016 Endocrine Society’s Guideline for PA management recommend that patients with a positive screening undergo one or more confirmatory tests to definitively confirm or exclude the diagnosis. Confirmatory testing procedures include oral sodium loading, saline infusion test (SIT), fludrocortisone suppression, captopril test (CT) and furosemide upright test (FUT). The FUT, mainly proposed by the Japan Endocrine Society, does not have limitation in patients with severe uncontrolled hypertension and heart failure. A positive FUT is defined as a plasma renin activity (PRA) <2 ng/mL/h after 2h, but it has not been standardized using a direct renin assay. The aim of this prospective study was to evaluate the FUT positive rate in a Brazilian cohort of PA patients and to establish a cut-off level to confirm PA diagnosis using direct renin concentration (DRC). We performed the FUT in 45 consecutive patients (25 males; median age 50 yrs, from 31 to 67 yrs) with PA diagnosis confirmed by biochemical cure after unilateral adrenalectomy or by adrenal venous sampling. Patients received furosemide 40 mg iv and stayed in upright position for 2h, starting at 8-9.30 AM. Blood samples for DRC, aldosterone, and potassium were drawn at time zero and after 2h. Aldosterone and DRC were measured by a chemiluminescent immunoassay (LIAISON®). Median A/DRC ratio was 10.3 (range, 2.54 to 66.4). Hypokalemia was evidenced in 27 out of 45 (60%) patients. Median DRC before and after 2h FUT was 2.8 uUI/mL (1.2 to 8.3) and 3.0 uUI/mL (0.5 to 19), respectively. Using the conversion factor of 12 to calculate PRA, FUT was positive (DRC/12= PRA <2 ng/mL/h) in all patients. Based on the highest renin level after FUT, the most suitable cut-off of direct renin concentration to confirm PA diagnosis was 20 uUL/mL. Additionally, potassium levels did not significantly change after FUT. Among these 45 PA patients, 39 performed an additional confirmatory test (recumbent SIT in 24 and CT in 15 patients). The positive rate for SIT was 83% using an aldosterone cut-off of 10 ng/dL and 100% using a cut-off of 6.8 ng/dL. CT and FUT were positive in all PA patients. In conclusion, FUT was a safe and reliable test for PA confirmation. In addition, we suggest a renin cut-off <20 uUI/mL after FTU to confirm PA diagnosis. Support: CNPq (403256/2016-0) to MQA