Xray affected joints for erosions<unk>  factor (positive in 60% to 70% of patients)
Anti-cyclic citrullinated peptide (CCP) antibodies (positive in about 70% of patients)
ANA
Consider arthrocentesis
WBC count typically 1,500-20,000
WBC count typically 1,500-20,000
Rheumatoid arthritis
Septic arthritis of previously injured joint
Reactive arthritis
Fibromyalgia
Juvenile idiopathic arthritis
Osteoarthritis
Lyme disease
Reactive poststreptococcal arthritis