Table 1.
Interpretation of adrenal venous sampling
| Index | Formula | Interpretation |
|---|---|---|
| Selectivity index | PCCside/PCCIVC | Values ≥3 confirm that the sample was obtained in the adrenal vein. |
| Lateralization index | (PACdominant/PCCdominant) (PACnondominant/PCCnondominant) |
Values >3 to 4 indicate lateralized aldosterone excess. |
| Contralateral suppression index | (PACnondominant/PCCnondominant) (PACIVC/PCCIVC) |
Values below the cutoff [1] indicate suppression of aldosterone secretion in the nondominant gland. |
In adrenal venous sampling (AVS), aldosterone and cortisol concentrations are measured in blood samples from 3 sites [right adrenal vein, left adrenal vein, and vena cava inferior (IVC)], often under continuous cosyntropin [synthetic adrenocorticotropic hormone (ACTH)] infusion. Absolute values and accurate laboratory assays for cortisol and aldosterone are essential for successful interpretation of the data. The plasma cortisol concentrations (PCC) from the adrenal veins and IVC are used to confirm successful cannulation of both adrenal veins. The calculated selectivity index (SI) is the most popular technique to confirm the success of AVS [43]. The finding of a concentration gradient between a blood sample in an adrenal vein and the IVC indicates the correct placement of the catheter’s tip into the adrenal vein. Most centres use an SI cut-off of 3 or greater for AVS performed during ACTH stimulation [43]. The lateralization index (LI; high-side adrenal vein PAC/PCC divided by low-side adrenal vein PAC/PCC) is the index used for assessment of lateralization of aldosterone excess and is the primary endpoint of AVS. Because of the dilutional effect of the samples by nonadrenal blood, the adrenal aldosterone levels are corrected by the plasma cortisol concentration. Most centers use LI between 3 and 4 during ACTH stimulation. Ratios ≤ 3 are consistent with bilateral aldosterone secretion [21,43]. In patients with unilateral disease the aldosterone/cortisol ratio for the nondominant adrenal is less than or equal to the corresponding ratio for the peripheral vein [21,44-46]. This is called “contralateral suppression” and confirms unilateral disease of the other adrenal gland.
Abbreviations: dominant, side with higher plasma aldosterone concentration; IVC, inferior vena cava, nondominant, side with lower plasma aldosterone concentration; PAC, plasma aldosterone concentration; PCC, plasma cortisol concentration.