Unstimulated protocol:
Selectivity index (SI) ≥ 2 confirms bilateral catheterization. Lateralization index (LI) ≥ 2 indicates unilateral disease; contralateral ratio (CR) < 1 provides supporting evidence. Perform in the morning after overnight recumbency.
Peripheral / IVC
Reference Sample
ng/dL
μg/dL
Right Adrenal Vein
Right AVS
ng/dL
μg/dL
Left Adrenal Vein
Left AVS
ng/dL
μg/dL
Calculated Results
SI — Right
—
Cortisol right / cortisol IVC
Threshold: ≥ 2 (unstimulated)
SI — Left
—
Cortisol left / cortisol IVC
Threshold: ≥ 2 (unstimulated)
A:C Right
—
Aldo/Cortisol ratio, right
A:C Left
—
Aldo/Cortisol ratio, left
A:C IVC
—
Aldo/Cortisol ratio, IVC
Lateralization Index (LI)
—
Higher A:C / Lower A:C
Threshold: ≥ 2 (unstimulated); ≥ 4 (cosyntropin)
Contralateral Ratio (CR)
—
Suppressed side A:C / IVC A:C
Threshold: < 1 supports unilateral disease
Interpretation Thresholds
| Index | Formula | Unstimulated | Cosyntropin-stimulated | Interpretation |
|---|---|---|---|---|
| Selectivity Index (SI) | Adrenal cortisol / IVC cortisol | ≥ 2 | ≥ 5 | Confirms adrenal vein catheterization; must be met bilaterally |
| Lateralization Index (LI) | Dominant A:C / Non-dominant A:C | ≥ 2 | ≥ 4 | LI ≥ threshold → unilateral disease, consider adrenalectomy |
| Contralateral Ratio (CR) | Suppressed side A:C / IVC A:C | < 1 | < 1 | Contralateral suppression supports unilateral aldosterone excess |
| A:C Ratio | Aldosterone (ng/dL) / Cortisol (μg/dL) | — | — | Corrects for dilution; basis for all ratio calculations |
Thresholds follow the 2025 Endocrine Society Clinical Practice Guideline (Adler et al., JCEM 2025) and the PASO criteria. The cosyntropin SI ≥ 5 threshold is specified in the 2025 guideline; the unstimulated SI range of 1.4–3 reflects center variability, with ≥ 2 used here as a widely applied consensus value. Some centers apply LI ≥ 4 for both protocols. Consult local institutional protocol.
Based on: Adler GK et al. (Endocrine Society), J Clin Endocrinol Metab 2025; Funder JW et al. (Endocrine Society), J Clin Endocrinol Metab 2016; Williams TA et al. (PASO), Lancet Diabetes Endocrinol 2018. This tool is intended as a clinical reference and does not replace physician judgment. AVS interpretation should be performed in the context of the complete clinical picture, institutional protocol, and multidisciplinary review.