Laurie, i did some reading & it turns out that there are indeed tests that measure neurotransmitter amounts, but none that measure the amount your brain is actively utilizing at any given day/hour/moment. for instance, because 80-90 percent of your serotonin is made in the digestive tract, they can test whether or not your body is deficient of creating serotonin in the GI, & they can use this information (in addition to psychoanalysis) to determine if you may have a deficiency in the brain. but, it's difficult to determine if your body is allowing absorption into the brain. the tests aren't completely fool proof because they can't determine our reuptake, how much serotonin is being utilized, or whether or not we've got issues with too few receptor synapses.