So far, there is no consensus based on numerous clinical trials on what "healty" levels of anti-oxidants are or what they should be. If a milligram is good, is a kilogram better? Unknown.
The Pharmanex company has a "BioPhotonic" Scanner that measures carotenoid levels(beta-carotine)by placing your hand on the device. They also promote a line of anti-oxidant products to take to "improve" your health, no matter what your levels are.
My opinion? The scanners are too expensive and are unnecessary. Keep on eating your fruits and vegetables, supplement with Vitamin C and E.