Aldo

Aldosterone

Hormones

What is Aldosterone?

Aldosterone is a steroid hormone produced by the zona glomerulosa of the adrenal cortex. It is the principal mineralocorticoid in the body, meaning its primary function is regulating sodium and potassium balance and, consequently, blood volume and blood pressure. Aldosterone acts on the distal tubules and collecting ducts of the kidneys, promoting sodium reabsorption (which draws water with it, increasing blood volume) and potassium excretion. This mechanism is essential for maintaining electrolyte homeostasis and hemodynamic stability.

Aldosterone secretion is regulated primarily by the renin-angiotensin-aldosterone system (RAAS). When blood pressure drops or sodium levels decrease, the kidneys release renin, which converts angiotensinogen to angiotensin I, subsequently converted to angiotensin II by ACE (angiotensin-converting enzyme). Angiotensin II stimulates aldosterone release. Potassium levels also directly regulate aldosterone—even small increases in serum potassium stimulate aldosterone secretion to promote potassium excretion. ACTH from the pituitary plays a minor regulatory role. The aldosterone-to-renin ratio (ARR) is the primary screening test for primary aldosteronism, one of the most common and underdiagnosed causes of secondary hypertension.

Why It Matters

Primary aldosteronism (Conn's syndrome) is now recognized as the cause of 5–15% of all hypertension cases and up to 20% of resistant hypertension. It was previously considered rare, but improved screening has revealed it is far more common than once thought. Patients with primary aldosteronism have significantly higher cardiovascular risk—including heart attack, stroke, atrial fibrillation, and heart failure—compared to patients with essential hypertension at the same blood pressure levels, because aldosterone causes direct cardiac, vascular, and renal damage beyond its blood pressure effects. Identifying and treating primary aldosteronism can cure or substantially improve hypertension and reduce cardiovascular risk.

Normal Reference Ranges

GroupRangeUnit
Upright/Seated Adults7–30ng/dL
Supine Adults3–16ng/dL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High Aldo Levels Mean

Common Causes

  • Primary aldosteronism (aldosterone-producing adrenal adenoma or bilateral adrenal hyperplasia)
  • Secondary aldosteronism (renal artery stenosis, heart failure, liver cirrhosis, nephrotic syndrome)
  • Dehydration or volume depletion
  • High-potassium diet
  • Renin-secreting tumors (rare)
  • Pregnancy (physiologically elevated)

Possible Symptoms

  • High blood pressure, often resistant to standard medications
  • Low potassium (hypokalemia) leading to muscle weakness and cramps
  • Frequent urination, especially at night (nocturia)
  • Excessive thirst
  • Fatigue and muscle weakness
  • Headaches
  • Metabolic alkalosis
  • Heart palpitations (from hypokalemia)

What to do: Elevated aldosterone should be evaluated with the aldosterone-to-renin ratio (ARR). In primary aldosteronism, aldosterone is high and renin is suppressed (ARR >30 with aldosterone >15 ng/dL). Confirmatory testing with oral salt loading, saline infusion, or fludrocortisone suppression test is recommended. Adrenal CT is performed to identify adenomas versus bilateral hyperplasia, followed by adrenal vein sampling if surgery is being considered—this is critical because CT can miss small adenomas or show incidentalomas. Unilateral aldosterone-producing adenomas are best treated with laparoscopic adrenalectomy (often curative), while bilateral hyperplasia is treated medically with mineralocorticoid receptor antagonists (spironolactone or eplerenone).

What Low Aldo Levels Mean

Common Causes

  • Primary adrenal insufficiency (Addison's disease)
  • Isolated hypoaldosteronism (hyporeninemic hypoaldosteronism, common in diabetic nephropathy)
  • ACE inhibitor or ARB therapy (appropriately suppressed)
  • High sodium intake
  • Congenital adrenal hyperplasia (certain types)
  • Heparin or low-molecular-weight heparin therapy

Possible Symptoms

  • Low blood pressure (orthostatic hypotension)
  • High potassium (hyperkalemia)
  • Dehydration and salt craving
  • Fatigue and weakness
  • Dizziness upon standing
  • Nausea
  • Heart rhythm abnormalities (from hyperkalemia)

What to do: Low aldosterone with hyperkalemia should be evaluated by measuring renin to determine whether the deficiency is primary (adrenal—low aldosterone with high renin, as in Addison's disease) or hyporeninemic (both renin and aldosterone are low, common in diabetes with mild kidney disease). Addison's disease requires mineralocorticoid replacement with fludrocortisone in addition to glucocorticoid replacement. Hyporeninemic hypoaldosteronism with mild hyperkalemia may be managed with dietary potassium restriction and low-dose fludrocortisone. Medication causes (heparin, NSAIDs, potassium-sparing diuretics) should be reviewed and adjusted if contributing.

When Is Aldo Testing Recommended?

  • When evaluating hypertension that is resistant to three or more medications
  • When hypertension is accompanied by unexplained hypokalemia
  • When hypertension develops before age 30 or is severe at onset
  • When an adrenal incidentaloma is found on imaging

Frequently Asked Questions

The ARR is the primary screening test for primary aldosteronism. It is calculated by dividing the plasma aldosterone concentration (in ng/dL) by the plasma renin activity (in ng/mL/hr) or direct renin concentration. An ARR greater than 30, with an aldosterone level above 15 ng/dL, is considered a positive screen. The ARR is important because aldosterone or renin alone can be misleading—aldosterone may be only mildly elevated in primary aldosteronism, and renin can be low for other reasons. The ratio captures the inappropriate relationship between the two. For accurate results, certain medications that affect the RAAS (beta-blockers, ACE inhibitors, ARBs, diuretics) ideally should be discontinued or switched to neutral alternatives before testing, under medical supervision.
Primary aldosteronism has historically been considered rare because doctors only screened patients with both hypertension and low potassium. However, studies now show that most patients with primary aldosteronism (60–70%) have normal potassium—hypokalemia is actually a late finding. The Endocrine Society guidelines now recommend screening all patients with resistant hypertension (uncontrolled on 3+ medications), moderate-to-severe hypertension, hypertension with hypokalemia, hypertension with adrenal incidentaloma, and early-onset hypertension. Despite these guidelines, screening rates remain low—estimated at less than 2% of eligible patients. Increased awareness and screening could identify millions of patients with a treatable and potentially curable cause of hypertension.
Many common medications interfere with aldosterone and renin measurements, potentially causing false positive or false negative results. Beta-blockers suppress renin and can cause a falsely elevated ARR. ACE inhibitors, ARBs, and direct renin inhibitors raise renin and can cause falsely low ARR (masking primary aldosteronism). Diuretics, especially spironolactone and eplerenone, significantly affect results and should be stopped 4–6 weeks before testing. Ideally, patients are switched to medications that minimally affect the RAAS—verapamil (calcium channel blocker), hydralazine, and doxazosin (alpha-blocker) are considered acceptable during testing. Potassium should be repleted to normal before testing, as hypokalemia suppresses aldosterone. Always discuss medication adjustments with your doctor before testing.

Related Biomarkers

KPotassiumNaSodiumCortisolCortisol

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.