Joint pain and stiffness can be caused by other medical conditions besides rheumatoid arthritis, including:

• Osteoarthritis (most common form of arthritis).
• Crystal deposits in the joint (gout and pseudogout).
• Lupus (systemic lupus erythematosus, or SLE).
• Polymyalgia rheumatica.
• Inflammation of blood vessels in the body (vasculitis).
• Spondyloarthropathies (such as Reiter's syndrome[reactive arthritis], ankylosing spondylitis, and psoriatic arthritis).
• Bacterial arthritis.
• Fibromyalgia.
• Lyme disease.
• Viral diseases such as HIV (human immunodeficiency virus).
• Torn cartilage in the joint.

Usually, a doctor will diagnose rheumatoid arthritis by evaluating your symptoms, understanding your past health, and doing certain blood tests to rule out other causes for your symptoms.