Re‐evaluation of the fludrocortisone test: duration, NaCl supplementation and cut‐off limits for aldosterone

Abstract

Objective. Primary aldosteronism (PA) is the most common form of secondary hypertension. Thus, the aims of this study were: (1) to clarify whether the fludrocortisone suppression test (FST), which confirms autonomous aldosterone secretion, is reliable when carried out during a shorter period of time and (2) to confirm the importance of NaCl supplementation. The cut‐off limits already obtained for aldosterone in healthy subjects during the FST were applied in hypertensive patients with a high aldosterone to renin ratio (ARR). Material and methods. The healthy subjects were allocated to three groups. Fludrocortisone was administered 4 times daily over 4 days and sodium chloride was supplemented in 3 different doses. The result was applied in 24 hypertensive patients, in 24 healthy subjects (10 women (23–38 years old) and 14 men (23–58 years old)) and in 24 patients with hypertension and high ARR (16 women (45–74 years old) and 8 men (56–73 years old)). Blood pressure, aldosterone, renin, potassium and sodium were measured. Results. After three days of FST, there was a significant decrease in the serum level of aldosterone in the healthy subjects, regardless of high or low sodium chloride supplementation (p<0.001). The decrease in serum aldosterone was significantly less pronounced in patients with PA than in healthy subjects and hypertensive patients without PA (p<0.001). The 95th percentile of plasma aldosterone at the end of the test was 225 pmol/L. Conclusions. The FST can be shortened to 3 days and a daily 500 mg NaCl supplementation is sufficient. A cut‐off value for aldosterone of 225 pmol/L after 4 days with FST is appropriate.