Aldosterone is secreted by the adrenal glands and plays a crucial role in maintaining blood volume and blood pressure. Its secretion is stimulated by angiotensin II, which is synthesized by the kidneys. Renin synthesis by the kidneys is activated, for example, by a drop in blood pressure. The role of renin is to promote the synthesis of angiotensin II and, therefore, the secretion of aldosterone. Any drop in blood pressure and/or blood volume is quickly corrected by activation of the renin-angiotensin-aldosterone system. Aldosterone levels are interpreted based on the posture (lying or standing) at the time of collection and can be affected by many medications as well as dietary salt intake. The aldosterone/renin ratio can be measured to eliminate the effect of posture and other interferences.
High levels of aldosterone in the blood or urine may be due to a benign tumour in the adrenal glands or to high renin secretion following a drop in blood pressure in the kidneys. Low levels of aldosterone may result from malfunctioning adrenal glands (Addison’s disease) or decreased renin production in the kidneys.