Aldosterone is a steroid hormone from the adrenal zona glomerulosa, controlled by the renin-angiotensin system.
Mechanism: Tells the kidneys to retain sodium and excrete potassium, controlling blood volume and blood pressure. Independent of the cortisol/HPA axis but produced in the same gland.
Lab range: 4–31 ng/dL standing.
Caveats: Low aldosterone (often paired with low cortisol in HPA dysfunction) presents as low blood pressure, salt cravings, dizziness on standing, and fatigue. Frequently overlooked. Test alongside renin for the full picture: the aldosterone:renin ratio is the standard diagnostic tool.