Riddle Me This

I live in the body. It’s a hit or miss. If you were to test me the results could be either negative or positive. Maybe? It depends on the damage you have done. Some people don’t even know. It can cause you a number of problems. It can be cured and once you find out. The best thing to do is take care of you. Your body will be very pleased.

I’m heavenly involved in the functioning of your bodily systems. What I’m I?