Adrenal vein sampling (AVS) is a specialized diagnostic procedure used to investigate primary aldosteronism, a condition where the adrenal glands produce too much aldosterone. This excess aldosterone can lead to high blood pressure and other health issues. AVS precisely identifies the source of this overproduction. By pinpointing whether the excess aldosterone originates from one or both adrenal glands, AVS provides important information that guides treatment decisions.
Why Adrenal Vein Sampling is Performed
AVS is performed for individuals diagnosed with primary aldosteronism when imaging studies, such as CT or MRI scans, do not clearly show whether one or both adrenal glands are overproducing aldosterone. While imaging can identify nodules or enlargements, it cannot definitively determine if these findings are functional, meaning they are actively secreting excess hormones. The procedure helps differentiate between unilateral disease, where one adrenal gland is responsible, and bilateral disease, involving both glands. This distinction is important because unilateral disease may be curable with surgery, while bilateral disease is managed with medication. AVS is considered highly sensitive and specific for this subtype diagnosis in specialized centers.
Key Measurements for Interpretation
During AVS, blood samples are collected from the veins draining each adrenal gland, and from a peripheral vein. Two primary hormones are measured: aldosterone and cortisol. Aldosterone is the hormone whose excessive production defines primary aldosteronism.
Cortisol, produced by both adrenal glands, serves as an internal control. By comparing cortisol levels between the adrenal veins and a peripheral vein, clinicians confirm correct catheter placement within the adrenal vein. This ensures the collected blood sample accurately reflects the hormone output of that specific gland.
Understanding the Interpretation Criteria
Interpreting AVS results involves calculating specific ratios to determine both sample adequacy and the source of aldosterone overproduction. The Selectivity Index (SI) is an important ratio used to confirm successful catheterization of the adrenal vein. It is calculated by dividing the cortisol concentration in the adrenal vein by the cortisol concentration in a peripheral vein or the inferior vena cava. A common cutoff for adequate sampling without adrenocorticotropic hormone (ACTH) stimulation is an SI of 2.0 or greater.
The Lateralization Index (LI) helps determine if one gland is producing significantly more aldosterone than the other. This index compares the aldosterone-to-cortisol ratio from the dominant adrenal vein to that from the non-dominant adrenal vein. A lateralization index greater than 4.0, particularly with ACTH stimulation, is commonly used to indicate unilateral aldosterone production. The use of cortisol in these ratios helps account for variations in blood flow and dilution, making the comparison more accurate.
The contralateral suppression index (CSI) also helps confirm that aldosterone secretion from the “normal” gland is appropriately suppressed. It compares the aldosterone-to-cortisol ratio from the non-dominant adrenal vein to the peripheral vein. An optimal CSI cutoff of 0.6 has been identified to detect unilateral primary aldosteronism.
What the Results Indicate
AVS results directly inform patient management. If AVS indicates unilateral aldosterone production, one adrenal gland is the primary source of excess aldosterone. Removing the affected gland could resolve the primary aldosteronism. Conversely, if AVS reveals bilateral aldosterone production, both adrenal glands contribute to the excess hormone, meaning surgery on one side would not address the problem.
In some instances, AVS may yield failed or inconclusive sampling results. This occurs when selectivity index criteria are not met, indicating inadequate blood samples for reliable interpretation. These cases may require a repeat procedure or further investigation. Rarely, AVS may indicate no aldosterone overproduction, despite initial suspicions of primary aldosteronism. This suggests the patient’s symptoms, such as high blood pressure, may be due to other underlying causes.
Next Steps After Interpretation
Following AVS interpretation, next steps are tailored to the diagnosis. If unilateral aldosterone production is confirmed, surgical removal of the affected adrenal gland, known as adrenalectomy, is discussed as a potential curative treatment. This procedure can improve blood pressure. For individuals with bilateral aldosterone production, treatment involves long-term management with mineralocorticoid receptor antagonist medications, such as spironolactone or eplerenone, to block aldosterone’s effects. If AVS is inconclusive or indicates no aldosterone overproduction, further investigations may identify other causes of high blood pressure or re-evaluate the initial diagnosis.