**3.2 Adrenal venous sampling**

There are an increasing number of reports that adenal vein sampling (AVS) is the gold standard test to differentiate unilateral from bilateral disease in patients with PAL. The Endocrine Society guidelines state that AVS is the "standard test to differentiate unilateral from bilateral causes of [primary aldosteronism]. 1 Adrenal venous sampling is a difficult procedure as the right adrenal vein is small, with the success rate depending on the proficiency of the angiographer. AVS is expensive, technically demanding and carries a tiny, but not negligible, risk of adrenal-vein rupture.36

In a study where AVS was used as the gold standard for diagnosis, CT scans mistakenly suggested that one-quarter of patients had an APA; correctly identified a unilateral or bilateral excess of aldosterone only in half of all patients; falsely suggested a bilateral adrenal hyperplasia in one-fifth of patients with a unilateral source of aldosterone excess; and in some patients identified an APA in the wrong adrenal gland.34

Rapid cortisol assays during AVS to monitor cortisol levels can reduce the failure rate of AVS. We have developed a new rapid cortisol assay using immunochromatography, in which cortisol concentrations can be measured within 6 min. (briefly explain false positive rates etc., in this method- should this be used in conjunction with CT?) Using this technique, the success rate of AVS has improved to 93% .37
