Aldosterone, which plays a crucial role in maintaining blood volume and blood pressure, is produced by the adrenal glands under the influence of angiotensin II. Renin is a protein produced in the kidneys, and its secretion 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. In normal individuals, any drop in blood pressure and/or blood volume is quickly corrected by activation of the renin-angiotensin-aldosterone system. This system can be disrupted by damage to either the renin secretion or the aldosterone secretion process. Measuring the aldosterone/renin ratio in the blood helps determine whether an increase in aldosterone levels is due to a condition directly affecting the adrenal glands or kidneys. The aldosterone/renin ratio is not dependent on the patient’s position (lying or standing) at the time of sample collection. Aldosterone levels higher than 400 picomoles per litre (pmol/L) are required for the ratio interpretation to be valid.
A high aldosterone/renin ratio is most often due to excessive aldosterone secretion by a benign adrenal tumour. All high or “grey area” results must be confirmed by other diagnostic tests.