Master the adrenal vein sampling protocol with evidence-based steps for patient selection, cannulation, and lateralization interpretation in primary aldosteronism.

Adrenal Vein Sampling Protocol: A Complete Interventional Radiology Guide

Introduction to adrenal vein sampling

The adrenal vein sampling protocol remains the definitive minimally invasive technique for distinguishing unilateral from bilateral aldosterone excess in patients with primary aldosteronism. Despite advances in cross-sectional imaging, computed tomography and magnetic resonance imaging fail to accurately subtype this condition in over one-third of cases, risking inappropriate adrenalectomy or missed surgical candidacy.^[1][2]

Performed by interventional radiologists under fluoroscopic guidance, AVS involves selective catheterization of the right and left adrenal veins to measure aldosterone and cortisol concentrations. The resulting lateralization index guides the critical decision between unilateral laparoscopic adrenalectomy and lifelong mineralocorticoid receptor antagonist therapy.^[3][4]

Clinical indications and patient selection

AVS is indicated for all patients with biochemically confirmed primary aldosteronism who are considering adrenalectomy and are appropriate surgical candidates, irrespective of adrenal imaging findings.^[3][5] The Endocrine Society guidelines emphasize that imaging alone should not determine laterality because nonfunctional adrenal incidentalomas coexist with bilateral hyperplasia in up to 40% of cases.

Specific exceptions where AVS may be omitted include patients younger than 35 years with florid biochemical evidence (aldosterone >550 pmol/L, suppressed renin, spontaneous hypokalemia) and a solitary unilateral adrenal nodule on CT.^[5][6] Patients with germline mutations causing familial hyperaldosteronism or adrenal lesions suspicious for cortical carcinoma should also bypass AVS in favor of direct surgical or oncologic management.

Pre-procedural assessment requires confirmation of autonomous aldosterone secretion through saline infusion suppression or captopril challenge testing.^[1][7] Hypokalemia must be corrected before sampling because low potassium suppresses aldosterone production and can mask lateralization.

Pre-procedural preparation and medication management

Meticulous medication withdrawal is essential to prevent confounding results. Mineralocorticoid receptor antagonists (spironolactone, eplerenone) should be discontinued for at least four to six weeks, while angiotensin-converting enzyme inhibitors and angiotensin receptor blockers require a minimum two-week washout.^[5][8] In selected patients with severe hypokalemia or uncontrolled hypertension, mineralocorticoid receptor antagonists may be continued if renin remains suppressed.^[5]

Cross-sectional imaging with thin-slice contrast-enhanced CT should be obtained before AVS to localize the right adrenal vein, characterize adrenal morphology, and exclude adrenocortical carcinoma.^[9][10] Modern CT techniques with optimized venous phase enhancement improve visualization of the right adrenal vein and can reduce both procedural time and radiation exposure.

Laboratory evaluation includes complete blood count, comprehensive metabolic panel, coagulation studies, and type-and-screen. Potassium repletion should target a serum level above 4.0 mEq/L. Fasting for six hours is standard, and intravenous access should be established before arrival in the angiography suite.

Vascular access and catheterization technique

Right common femoral vein access is the standard approach, utilizing a 4–5 French vascular sheath.^[4][11] The right adrenal vein is cannulated first because it is technically more demanding; minimizing the interval between right and left sampling to less than five minutes reduces biological variability when simultaneous sampling is not feasible.^[5][12]

The right adrenal vein drains directly into the posterolateral wall of the inferior vena cava between the T11 and L1 vertebral levels. It is characteristically short, sharply angled, and prone to spasm. A 4–5 French Cobra or Simmons catheter provides the primary engagement platform, though a microcatheter is frequently required for final selective intubation.^[4][11] A side-hole placed 2–3 mm from the catheter tip facilitates gentle aspiration and reduces vessel collapse from suction.

The left adrenal vein shares a common trunk with the left inferior phrenic vein before draining into the superior aspect of the left renal vein. Cannulating this common trunk is preferred to avoid superselective engagement of the inferior phrenic vein alone.^[4][11] Once positioned, gentle hand injection of 2–3 mL contrast confirms the characteristic caput medusae appearance of emissary veins from the adrenal capsule.

Departments performing high volumes of diagnostic venous sampling benefit from standardized catheter and guidewire inventories. SATPro interventional kits bundle the diagnostic catheters, microcatheters, and hydrophilic wires required for complex venous anatomy, while SATLine extension tubing maintains closed-system integrity during multi-site sampling.

Imaging parameters and contrast protocol

Fluoroscopy with digital subtraction angiography at 3–6 frames per second provides real-time guidance for catheter manipulation and venographic confirmation.^[4][13] Pre-procedural CT with 1 mm slice thickness in the venous phase serves as a roadmap, identifying the right adrenal vein origin and any variant anatomy such as accessory hepatic veins that may mimic the target.

Contrast administration is minimal compared with arterial interventions. A renal or inferior vena cava venogram requires 10–15 mL of non-ionic iodinated contrast injected at 5–8 mL/s. Selective adrenal venography uses only 2–3 mL per side, hand-injected to confirm position and assess the caput medusae pattern.^[4][11] Total contrast burden typically remains below 50 mL, preserving renal safety in this hypertensive population.

Intraprocedural DynaCT or cone-beam CT is increasingly utilized to confirm adrenal gland enhancement during right adrenal vein cannulation, improving first-pass success and reducing procedural time.^[13][14] When available, DynaCT after injection of 3 mL diluted contrast directly verifies catheter position within the adrenal vein.

Cosyntropin stimulation and sampling strategy

Cosyntropin (synthetic ACTH) stimulation is recommended during AVS because it increases cortisol secretion from both adrenal glands, enlarging the gradient between adrenal vein and peripheral cortisol concentrations and improving recognition of successful cannulation.^[5][15] A typical protocol administers 250 mcg intravenously as a bolus followed by a 50 mcg/hour continuous infusion beginning 30 minutes before sampling.

Simultaneous bilateral sampling is the preferred technique, avoiding temporal fluctuations in aldosterone and cortisol that can confound sequential collection.^[5][12] When sequential sampling is necessary due to equipment limitations, the right adrenal vein must be sampled first, with left-sided collection completed within five minutes.^[5]

Blood samples are drawn from both adrenal veins and a peripheral vein (inferior vena cava or femoral vein) into chilled tubes for aldosterone and cortisol assay. Rapid point-of-care cortisol testing can improve cannulation success rates from approximately 64% to 84%, particularly for non-ACTH-stimulated protocols and less experienced operators.^[16][17]

Interpretation of results and lateralization indices

Successful cannulation is confirmed by the selectivity index (SI), defined as the ratio of adrenal vein cortisol to peripheral vein cortisol. An SI ≥2 on unstimulated sampling or ≥5 after cosyntropin stimulation confirms that the sample reflects adrenal venous effluent rather than diluted inferior vena cava blood.^[5][11] Studies without at least one selective sample are considered non-diagnostic.

The lateralization index (LI) determines unilateral versus bilateral disease. It is calculated as the aldosterone-to-cortisol ratio on the dominant side divided by the same ratio on the contralateral side. An LI ≥4 indicates unilateral aldosterone excess and predicts surgical cure.^[3][5] The contralateral suppression index (CSI), calculated by dividing the non-dominant adrenal A/C ratio by the peripheral A/C ratio, should be <1 to confirm suppression of the unaffected gland.^[5][18]

Approximately 8–36% of successful AVS studies show no lateralization, indicating bilateral disease or technically suboptimal sampling.^[18][19] In such cases, repeat AVS with ACTH stimulation, adrenal vein localization by CT, or experienced operator review is recommended before committing to medical management.

Complications and risk mitigation

Adrenal vein sampling is generally safe, with major complications occurring in fewer than 5% of procedures.^[4][20] The most common adverse event is right adrenal vein rupture from forceful contrast injection or aggressive catheter manipulation, reported in 4–10% of cases. Most ruptures are self-limiting, though adrenal hemorrhage can cause severe flank pain persisting for 48–72 hours and may permanently destroy the gland.

Adrenal hemorrhage occurs in 2–5% of procedures and is usually detected on post-procedural imaging.^[20][21] Risk factors include difficult cannulation, vessel dissection, and excessive contrast injection pressure. Adrenal vein thrombosis, access site hematoma, vasovagal response, and contrast-induced nephropathy represent additional but less frequent complications.

Radiation protection is paramount during AVS because right adrenal vein cannulation can require 15–45 minutes of fluoroscopy time. SATPro radiation protection aprons and scatter-shielding systems attenuate >70% of scatter radiation at 80 kV, protecting interventional radiologists and radiographers during prolonged diagnostic procedures.

Follow-up protocol and clinical outcomes

Patients with unilateral lateralization should be referred for laparoscopic adrenalectomy, which cures hypertension in 30–60% of cases and improves blood pressure control in 80–90%.^[22][23] Complete biochemical cure, defined as normalization of aldosterone-to-renin ratio without antihypertensive medication, occurs in approximately 40–50% of patients.

Those with bilateral disease or failed cannulation are managed medically with spironolactone or eplerenone. Follow-up includes monitoring potassium, creatinine, and blood pressure at 1, 3, and 6 months post-procedure. Patients who undergo adrenalectomy require endocrine follow-up to assess for contralateral gland recovery and resolution of hypokalemia.

Quality of life improves significantly after AVS-directed management, particularly in surgically treated patients who experience reduced antihypertensive burden and resolution of hypokalemia.^[24][25] Long-term cardiovascular outcomes also favor unilateral adrenalectomy over medical therapy alone.

Conclusion

The adrenal vein sampling protocol remains an indispensable tool in the contemporary management of primary aldosteronism. When performed by experienced interventional radiologists using simultaneous bilateral sampling with cosyntropin stimulation, AVS achieves technical success exceeding 90% and provides definitive lateralization data that imaging alone cannot replicate.

Success depends on meticulous patient preparation, gentle catheter technique for the challenging right adrenal vein, and rigorous interpretation of selectivity and lateralization indices. Departments that standardize their equipment inventories—from SATPro sterile kits to SATMix preparation systems—consistently achieve higher first-pass cannulation rates and shorter procedure times.

As algorithm-based pre-screening tools evolve, AVS will remain the gold standard for surgical decision-making in primary aldosteronism, ensuring that patients with unilateral disease receive curative adrenalectomy while those with bilateral hyperplasia are directed toward optimal medical therapy.

Further reading

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2. Prostate Artery Embolization: Complete 2026 Protocol
3. Uterine Artery Embolization: Complete 2026 Protocol
4. TACE 2026: Complete Clinical Protocol Guide
5. Y-90 Radioembolization 2026: Complete TARE Protocol Guide

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