I've read online about C4 lab tests and how if it's elevated it can indicate arthritis....have any of you heard of this and has anyone known of this test and had an elevated result?The complement system is involved in the inflammatory process. My C3 and C4 were two (of the many) blood tests my RD ran when I first saw him. My C3 was increased. The levels are usually high when inflammation is present - similar to the C-Reactive Protein test. So, while the increased numbers can tell your RD something is wrong, it doesn't specifically tell your RD it's RA.