Changes of what? There are millions of parameters that affect each other in a nonlinear fashion due to genetics, environment, diet etc. Getting such data from the living system would be prohibitively invasive, blood tests have their limitations and doesn't provide real-time data.
I don't know what can be or should be measured. The idea is to develop better techniques for monitoring the body. A future tricorder X-Prize, for instance: http://tricorder.xprize.org
You're telling me what we can do today. I'm asking what we can develop to solve the problem.
