# Adrenal Vein Sampling > Adrenal vein sampling for NEET-PG Surgery: lateralising primary aldosteronism, selectivity and lateralisation indices, cosyntropin protocols. - Canonical URL: https://prepelephant.com/topics/neet-pg/surgery/adrenal-vein-sampling - Exam / course: NEET-PG · Subject: Surgery - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Adrenal Vein Sampling", PrepElephant, https://prepelephant.com/topics/neet-pg/surgery/adrenal-vein-sampling ## Direct answer Adrenal vein sampling (AVS) is the procedure that determines whether primary aldosteronism is driven by one adrenal (unilateral adenoma or unilateral hyperplasia, curable by adrenalectomy) or both (bilateral hyperplasia, treated medically with mineralocorticoid receptor antagonists). It is performed when primary aldosteronism is confirmed biochemically and surgery is contemplated, because CT misclassifies the culprit side in an appreciable fraction of patients — non-functioning adenomas are common incidental findings in older adults. Bilateral adrenal venous catheterisation samples cortisol and aldosterone from each vein: a selectivity index confirms cannulation, a lateralisation index identifies the secreting side. ## What you must remember - Indication: confirmed primary aldosteronism (ARR screening, confirmatory testing) in patients who are candidates for unilateral adrenalectomy — AVS assigns subtype, not diagnosis. - The right adrenal vein drains directly into the IVC, making it the technical challenge of catheterisation; the left enters the left renal vein via a common trunk. - Selectivity index: adrenal-vein to peripheral-vein cortisol ratio — commonly above 2 (with cosyntropin stimulation, higher thresholds near 5 are used in some protocols) confirms successful catheterisation. - Lateralisation index: ratio of aldosterone-to-cortisol ratios between the two sides; commonly used thresholds are around 2-4, with stimulated protocols using higher cut-offs — exact numbers vary by centre and stimulatory protocol. - Contralateral suppression (aldosterone-to-cortisol on the suppressed side below peripheral levels) supports unilateral disease. - CT may misdirect surgery: a visible nodule may be a non-functioning incidentaloma while the opposite gland hypersecretes — the central justification for AVS. - Adrenalectomy outcomes: hypokalaemia is corrected in nearly all; hypertension is cured in roughly 40-60 per cent and improved in most of the rest. - Exceptions where some guidelines allow skipping AVS: younger patients (under about 35-40) with a clear unilateral adenoma on CT, a normal contralateral gland and florid biochemistry. - Prepare by correcting hypokalaemia and withholding mineralocorticoid antagonists for weeks beforehand — they falsely raise renin. ## How the procedure reasons through, case by case A 44-year-old with resistant hypertension and hypokalaemia has a confirmed aldosterone-renin ratio and a CT showing a 1.4 cm left adrenal nodule. The reflex "adrenalectomise the nodule" is exactly what AVS exists to test. Under fluoroscopy, both adrenal veins are catheterised; cosyntropin is infused in many centres to stabilise cortisol secretion (it eases confirmation of selectivity, though protocols differ). Samples from each adrenal vein and a peripheral vein are analysed for cortisol and aldosterone. The arithmetic runs: first, selectivity — each adrenal-vein cortisol must sit convincingly above peripheral; if the right sample is actually IVC blood, the study is non-diagnostic on that side and must be repeated, not interpreted. Second, lateralisation — a strongly asymmetric aldosterone-to-cortisol ratio (by the centre's threshold) with contralateral suppression lateralises disease to the left, and laparoscopic left adrenalectomy follows. Third, if both sides secrete symmetrically, the diagnosis is bilateral hyperplasia and the answer is lifelong medical therapy with spironolactone or eplerenone — removing an adrenal would help nothing. The pre-procedure checklist is examinable: correct potassium (hypokalaemia suppresses aldosterone and muddies results), pause mineralocorticoid antagonists for an adequate washout with alternative antihypertensives, and consent for adrenal vein catheterisation risks including haemorrhage and dissection. ## Where students slip The most common conceptual error is treating AVS as a diagnostic test for Conn syndrome; the diagnosis is already made biochemically, and AVS answers only "which side" — the examiner's phrase "confirmed primary aldosteronism" in the stem is the clue. The second slip is skipping straight from CT nodule to theatre; in an older hypertensive population, incidental nodules are common and the functioning side may be the opposite one. The third is forgetting the drug washout and potassium correction — results from a patient on spironolactone with a potassium of 2.8 are uninterpretable, and saying so earns more marks than any number. ## Frequently asked questions ### Why is adrenal vein sampling performed in primary aldosteronism? To lateralise aldosterone excess — distinguishing a unilateral source amendable to adrenalectomy from bilateral hyperplasia best treated medically — because CT cannot reliably make the distinction. ### What is the selectivity index? The adrenal-vein to peripheral-vein cortisol ratio, confirming successful catheterisation of each adrenal vein (commonly above 2 without stimulation, with higher thresholds after cosyntropin). ### How good is CT at identifying the culprit side in primary aldosteronism? Unreliable — it misclassifies laterality in a meaningful fraction of patients because non-functioning nodules are common and bilateral disease is under-recognised on imaging. ### What are the outcomes of adrenalectomy for unilateral disease? Hypokalaemia corrects in nearly all patients, and hypertension is cured in roughly 40-60 per cent with improvement in most others, depending on duration and severity of hypertension. ### Which patients may forego AVS before surgery? Selected younger patients (commonly under about 35-40 years) with a clear unilateral adenoma, a biochemically normal-appearing contralateral gland and confirmed marked aldosterone excess — a guideline-sanctioned exception.