There are blood and urine tests called Estrogen Metabolism test that can determine not only if one is estrogen positive like tissue testing during or after surgery but the levels of the different kinds of estrogen people have in their bodies. Estrogen levels can change over time. Even if a person starts off as ER positive it doesn't mean that person will still be ER positive several years later. If you are considering reducing or changing your AIs you might want to consider one of these tests.
Sometimes the results also include a food list to improve estrogen levels.
Some insurance companies will pay for the test and some will not, so it is better to check if you are considering this option.
http://www.rmalab.com/index.php?id=52
http://www.genovadiagnostics.com/ind...&nav=doc&id=17
I had these tests 3 -4 times over the years and was able to monitor and improve my estrogen levels quite well.
I found the test reliable for my needs.