C-reactive protein, or CRP, is a protein found in the blood when there is an acute inflammation of some sort in the body. It isn't indicative of UC or lupus or any other specific disease by itself, only that there is an inflammation somewhere.
The ANA (antinuclear antibody) test looks for specific antibodies that indicate the presence of an auto-immune condition, such as rheumatoid arthritis, lupus, UC or a host of other conditions.
Specific combinations of labs can point to one disease or another, but I don't know all the intricacies of that. There is a test called the LE prep that looks for certain cells that are specific to lupus and a limited number of other autoimmune disorders.
I don't know whether lupus can specifically mimic UC or not, but it does mimic a lot of other diseases. And it's pretty generally accepted that a person who has one autoimmune disorder is more likely to develop others. My private pet (completely unscientific) theory is that I have a disease called autoimmunity, which sometimes chooses to affect my airway and then is called asthma, sometimes chooses to attack my thyroid and is called Graves disease, and now is attacking my colon and being called UC.
Hope this helps, and good luck to you.
Left-sided UC diagnosed 2001. Taking Colazal and Imuran, Remicade infusions and moving into remission. Finally off steroids after four years!
Now in remission for almost two years. Remicade has been my wonder drug.
"If you spend your time second-guessing your past decisions, you'll never have time to enjoy today."