Additional evaluation usually indicated for monarticular, traumatic, inflammatory, or chronic conditions or for conditions accompanied by neurologic changes or systemic manifestations.

• For all evaluations: include CBC, ESR, or C-reactive protein
• Where there are suggestive clinical features, include: rheumatoid factor, antibodies to cyclic citrullinated peptides (anti-CCPs), ANA, antineutrophil cytoplasmic antibodies (ANCA), antistreptolysin O titer, Lyme antibodies
• Where systemic disease is present or suspected: renal/hepatic function tests, UA
• Uric acid: useful only when gout diagnosed and therapy contemplated
• CPK, aldolase: consider with muscle pain, weakness
• Synovial fluid aspiration and analysis: always indicated for acute monarthritis or when infectious or crystal-induced arthropathy is suspected. Should be examined for (1) appearance, viscosity; (2) cell count and differential (suspect septic joint if WBC count >50,000/µL); (3) crystals using polarizing microscope; (4) Gram's stain, cultures (Fig. 47-2).