C-reactive protein and C3 lab tests--what are they for?

2 different tests. C-reactive protein is often used as a marker of inflammation--any disease process causes inflammation in the body, the CRP tend to be higher..I.E infections, active, rheumatoid arthritis, during heart attack etc... C3 is a specific protein (complement3), one of few protein groups that complement(help) antibodies/phagocytes to clear infection etc..I.E c3 defifiency is disease state. Hope this helps.