Does rheumatoid arthritis always show up in blood work?

No: If you mean are the antibodies associated with rheumatoid arthritis (ccp and rf) always positive in rheumatoid arthritis, no. About 15% of patients are "seronegative." usually there are some abnormalities though such as elevated inflammatory markers, anemia, elevated white count or elevated platelets. But not always.

Possible negative: Rheumatoid factor (rf) and cyclic citrinullated peptide (ccp) are the two tests that help confirm a diagnosis of rheumatoid arthritis. Other tests are done to measure inflammation, determine which drugs may be used, etc. About 15% of people with RA are rf and ccp negative.