yes the signs and symptoms of most diseases are only warning signs of the damage that is happening inside the body, think of it this way the signs are things you can measure such as blood glucose levels or blood pressure, symptoms are how you feel, i feel dizzy or my head hurts. Some of the most dangerous diseases such as heart problems, STDs and many more have no signs or symptoms but they still have serious effects to the body, so the only way to get the info a person would need is to go and get lab tests done to ensure their body is functioning normally, like your liver for example you are not going to feel your liver having problems until you go into liver failure so the way one watches for problems is blood work and lab tests!