How is Gout Diagnosed?
The demonstration of MSU crystals in aspirates of synovial fluid or tophi remains the gold standard for diagnosis. Intracellular or extracellular MSU crystals are needle-shaped, approximately the size of a white blood cell, and are strongly negatively birefringent (yellow when parallel to the axis of a red compensator) on polarized microscopy (Arthrocentesis and Synovial Fluid Analysis). MSU crystals can be identified in joint aspirates during intercritical (asymptomatic) periods. Synovial fluid during a gout flare is inflammatory (typically 20,000–100,000 leukocytes/mm 3 ) with a predominance of neutrophils. Septic synovial fluids may contain MSU crystals; therefore, it is important to obtain a Gram stain and culture to rule out concomitant septic arthritis. This is particularly important as gout flares may present with overlapping signs and/or symptoms of infection such as low-grade fever, elevated acute phase responses, and mild leukocytosis.