How to tell the difference between systemic lupus erythematosus or rheumatoid arthritis?

Lab: Signs, symptoms, sophisticated specific lab testing.

Sometimes hard: Both have arthritis as part of the disease in RA it is the major feature and most people have nothing else. Lupus, while having arthritis as part of it, often has many other features of other organ systems like the skin kidneys bervous system or blood best way is to see a rheumatologist.