When performing adrenal vein sampling, is calculating selectivity index using androstenedione superior to using cortisol alone for determining successful catheterization?  

In our experience, the measurement of androstenedione is particularly beneficial when the AVS is done without Cosyntropin stimulation. While the cortisol gradient may be <2 in such cases, we see a several-fold increase in Androstenedione gradients confirming successful catheterization.