Investigations (Gout)1st tests to order

Arthrocentesis with synovial fluid analysis

Confirms diagnosis, excludes septic arthritis and differentiate gout from pseudogout Result: WCC count > 2.0 x 109/L (with >80% PMNs) Strongly negative birefringent needle-shaped crystals under polarized light

Tests to consider

Uric acid level Obtained at least 2 weeks after attack resolves, as it may be falsely low or normal during the attack Gout can develop with levels lower than the upper limit of normal values Results: >416 micromol/L in men >357 micromol/L in women

X-ray of affected joint Hands are optimal place to look gouty erosions Usually normal in acute gout Well-demarcated erosions seen in chronic or tophaceous gout Results: Periarticular erosions (may have an overhanging edge or punched-out appearance) Tophi visible on x-rays as soft tissue swellings

Erosive arthritis in chronic gout. Punched-out erosions are visible (arrows), in association with a destructive arthritis affecting the first metatarsophalangeal joint.

Ultrasound US-detected erosions are most commonly found in 1st MTP joint and MCP joints Results: Erosions Tophi Double-contour line