Adrenal vein sampling

Adrenal vein sampling (AVS) is a specialised diagnostic procedure used to determine the source of excess hormone production in patients with primary aldosteronism (PA), also known as Conn’s syndrome. PA is a condition characterised by overproduction of aldosterone hormone by the adrenal glands, leading to high blood pressure and electrolyte imbalances. AVS helps differentiate between unilateral (one adrenal gland) and bilateral (both adrenal glands) causes of aldosterone excess, guiding treatment decisions. 

Indications

Adrenal vein sampling is indicated for patients with:

1. Primary Aldosteronism (Conn’s Syndrome): Excessive production of aldosterone hormone by the adrenal glands, leading to hypertension and electrolyte imbalances.
2. Suspected Unilateral Aldosterone Production: To determine if one adrenal gland (unilateral) is primarily responsible for aldosterone excess, indicating a potential surgical cure (adrenalectomy).

Pre-procedure Preparation

1. Hormone Evaluation:
   • Measurement of aldosterone and renin levels to confirm the diagnosis of primary aldosteronism.
   • Blood pressure monitoring and assessment of electrolyte levels (potassium, sodium) to evaluate the effects of aldosterone excess.
2. Imaging Studies:
   • CT scan or MRI of the adrenal glands to visualise their anatomy and identify any abnormalities, such as adrenal adenomas or hyperplasia.
3. Medication Management:
   • Discontinuation or modification of medications that may interfere with aldosterone or renin levels, such as antihypertensives (especially spironolactone) and diuretics.

Procedure Steps

1. Preparation:
   • The patient is typically admitted to a hospital or specialised centre for the procedure.
   • Intravenous access is established for medications and contrast dye administration.
2. Anaesthesia:
   • Local anaesthesia is used to numb the insertion site (usually the groin area).
3. Catheterization:
   • A catheter is inserted into the femoral vein (in the groin) under fluoroscopic guidance.
   • The catheter is navigated through the venous system until it reaches the adrenal veins, which drain blood from the adrenal glands into the vena cava.
4. Blood Sampling:
   • Once the catheter is in position within the adrenal veins (usually right and left sides), blood samples are simultaneously collected from both adrenal veins and a peripheral vein (usually from the inferior vena cava) for comparison.
   • Blood samples are analysed for aldosterone and cortisol levels to assess hormone production from each adrenal gland.
5. Contrast Injection:
   • Contrast dye may be injected through the catheter into the adrenal veins to visualise their anatomy and ensure accurate sampling.
6. Post-procedure Care:
   • The catheter is removed, and pressure is applied to the insertion site to prevent bleeding.
   • Patients are monitored for any immediate complications, and post-procedure instructions are provided.

Interpretation of Results

• Lateralization: Comparison of aldosterone levels between the right and left adrenal veins helps determine if one adrenal gland is producing significantly more aldosterone than the other.
• Selectivity Index: Calculation of a selectivity index (ratio of aldosterone concentration in the adrenal vein to that in the inferior vena cava) helps ensure accurate sampling and interpretation of results.
• Unilateral vs. Bilateral Aldosterone Production: Higher aldosterone levels in one adrenal vein (unilateral) suggest an adenoma or hyperplasia in that gland, while similar levels in both adrenal veins (bilateral) indicate hyperplasia or a non-surgically curable cause.

Benefits

• Accurate Diagnosis: Helps differentiate between unilateral and bilateral causes of primary aldosteronism, guiding treatment decisions.
• Surgical Planning: Identifies patients who may benefit from adrenal gland surgery (adrenalectomy) to cure aldosterone excess.
• Personalised Treatment: Allows for targeted and personalised management based on the underlying cause of primary aldosteronism.

Risks and Considerations

• Bleeding: Risk of bleeding or hematoma at the catheter insertion site.
• Infection: Risk of infection at the catheter site, though uncommon with proper sterile techniques.
• Adrenal Vein Dissection: Rarely, there may be difficulties in catheterizing the adrenal veins or obtaining accurate samples.

Conclusion

Adrenal vein sampling is a valuable diagnostic tool for evaluating primary aldosteronism and determining the underlying cause of aldosterone excess. By differentiating between unilateral and bilateral adrenal gland involvement, AVS guides treatment decisions, especially regarding the potential for surgical cure with adrenalectomy in select patients. Close collaboration between endocrinologists, interventional radiologists, and other specialists is crucial for the successful performance and interpretation of AVS results in patients with primary aldosteronism.