Step 1 topics → Endocrine → Hyperaldosteronism (Conn Syndrome)

Hyperaldosteronism (Conn Syndrome)

USMLE Step 1 trap: Predicts elevated renin in primary hyperaldosteronism rather than the suppressed renin that defines it. In primary hyperaldosteronism, autonomous aldosterone secretion suppresses renin via negative feedback, resulting in a high aldosterone-to-renin ratio with low renin.

Hyperaldosteronism is excess aldosterone production — and the key split is whether the adrenal gland is acting autonomously (primary) or responding to a legitimate signal (secondary). USMLE Step 1 hammers the primary form hard, especially the aldosterone-to-renin ratio, the triad of HTN + hypokalemia + metabolic alkalosis, and the management split between unilateral adenoma versus bilateral hyperplasia. The concept seems straightforward until the exam puts you in a vignette with a hypertensive patient on a diuretic and asks you to sort out the renin direction — that's where students consistently get wrecked.

The exam tests this from multiple angles. Pure recall shows up as: what's the aldosterone-to-renin ratio in primary vs secondary disease? Application gets harder: given a set of labs, can you identify which type of hyperaldosteronism is present and why renin is suppressed rather than elevated? Passage-based questions may hand you a patient with refractory hypertension, low potassium, and a 'normal' aldosterone value, and ask you to interpret the ratio — not just the absolute number. Step 1 loves the mechanistic chain here: aldosterone acts on the principal cell → Na+ retention → volume expansion → HTN, while K+ and H+ are lost in the collecting duct → hypokalemia and alkalosis.

The tricky parts cluster around three areas. First, students flip the renin direction in primary disease — they reason that high aldosterone must mean high renin drove it, which reverses the whole primary/secondary distinction. Second, students attribute the metabolic alkalosis entirely to hypokalemia, missing that aldosterone directly drives H+ secretion in the collecting duct. Third, students apply the surgical answer (adrenalectomy) to all primary hyperaldosteronism, when bilateral adrenal hyperplasia specifically requires medical management. Nail these three and you've handled the majority of what USMLE Step 1 can throw at this topic.

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Common misconceptions

Common mistake
Wrong: Primary hyperaldosteronism causes elevated renin because aldosterone is elevated.
Right: In primary hyperaldosteronism, autonomous aldosterone secretion suppresses renin via negative feedback, resulting in a high aldosterone-to-renin ratio with low renin.
In primary hyperaldosteronism, the adrenal gland fires on its own — aldosterone is elevated for autonomous reasons, not because renin told it to. That high aldosterone causes volume expansion, which suppresses the renin-angiotensin system via negative feedback. So renin ends up low, and the aldosterone-to-renin ratio is high. This is the defining lab signature of primary disease. Secondary hyperaldosteronism is the opposite: something (like renal artery stenosis) drives renin up, which legitimately drives aldosterone up — both are elevated together.
Common mistake
Wrong: The metabolic alkalosis in hyperaldosteronism is caused by hypokalemia alone.
Right: Metabolic alkalosis in hyperaldosteronism results from aldosterone-driven H+ secretion in the collecting duct (via H+-ATPase) and is worsened by hypokalemia-induced intracellular acidosis promoting further H+ excretion.
Aldosterone has a direct, independent effect on acid-base balance: it upregulates H+-ATPase in the alpha-intercalated cells of the collecting duct, driving proton secretion and generating new bicarbonate. That's the primary driver of metabolic alkalosis. Hypokalemia makes it worse — when K+ leaves cells, H+ enters to maintain electroneutrality, causing intracellular acidosis that signals the kidney to excrete even more H+. But blaming hypokalemia alone misses the direct renal acid-secreting action of aldosterone, which the exam specifically wants you to know.
Common mistake
Wrong: All cases of primary hyperaldosteronism should be treated surgically.
Right: Unilateral aldosterone-producing adenoma (Conn syndrome) is treated with adrenalectomy, while bilateral adrenal hyperplasia is managed medically with mineralocorticoid receptor antagonists (spironolactone or eplerenone).
The surgery-versus-medicine decision in primary hyperaldosteronism hinges entirely on whether the source is unilateral or bilateral. A unilateral aldosterone-producing adenoma (classic Conn syndrome) is a discrete lesion you can remove — adrenalectomy is potentially curative. Bilateral adrenal hyperplasia has no discrete target, so surgery won't fix it; instead, you block the receptor with spironolactone or eplerenone. This is why adrenal vein sampling matters: it differentiates these two before you commit to an operation.
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What the exam tests

  1. Understand the mechanistic chain: how excess aldosterone causes sodium retention, volume-dependent hypertension, renal potassium wasting, and both direct and hypokalemia-worsened metabolic alkalosis.
  2. Distinguish primary from secondary hyperaldosteronism by their etiologies — aldosterone-producing adenoma and bilateral adrenal hyperplasia versus renovascular disease, renin-secreting tumors, and physiologic states like heart failure or cirrhosis.
  3. Interpret the aldosterone-to-renin ratio as the screening tool: a high ratio (elevated aldosterone, suppressed renin) points to primary disease, while elevated aldosterone with elevated renin points to secondary disease.
  4. Select the correct management based on subtype: unilateral adenoma goes to adrenalectomy (confirmed by adrenal vein sampling first), while bilateral adrenal hyperplasia is treated medically with mineralocorticoid receptor antagonists like spironolactone or eplerenone.

Can you avoid these mistakes?

A 45-year-old woman has hypertension, K+ of 3.1 mEq/L, and metabolic alkalosis. Labs show aldosterone 28 ng/dL and plasma renin activity 0.3 ng/mL/hr. What is the most likely diagnosis, and what does the renin level tell you about the mechanism?
Explain step by step how excess aldosterone produces metabolic alkalosis — specifically, which cell type is directly involved and what role hypokalemia plays on top of that.
A patient is diagnosed with primary hyperaldosteronism. CT scan shows no discrete adrenal mass. What is the next diagnostic step, and what treatment follows if the results confirm the suspected etiology?
A patient with cirrhosis and ascites has elevated aldosterone and elevated plasma renin activity. How does this differ from Conn syndrome mechanistically, and what drives the aldosterone elevation in this case?

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