What is the aldosterone to renin ratio in cases of secondary hyperaldosteronism?

In cases of secondary hyperaldosteronism, the aldosterone to renin ratio is typically low, which can be surprising compared to what one might expect. Secondary hyperaldosteronism occurs when there is increased renin production due to factors such as renal artery stenosis or heart failure that leads to effective volume depletion. In these situations, the body compensates by increasing aldosterone secretion in an attempt to retain sodium and water and normalize blood pressure.

However, because the renin levels are elevated due to the underlying condition, the aldosterone to renin ratio becomes low. This is a critical distinction in understanding hyperaldosteronism types, as a high aldosterone to renin ratio typically indicates primary hyperaldosteronism (such as in Conn's syndrome), where aldosterone secretion is autonomous and not regulated by renin. In secondary forms, the high renin levels dilute the aldosterone concentration, leading to a low ratio despite having high levels of aldosterone in absolute terms. This ratio therefore helps clinicians differentiate between primary and secondary causes of hyperaldosteronism.