Gout laboratory tests

A definitive diagnosis of gout is made from light microscopy of the fluid aspirated from the joint. The fluid demonstrates intracellular negatively bi-refringent monosodium urate crystals and polymorphonuclear leukocytes in the synovial fluid. Although hyperuricemia is a common feature of gout, a high uric acid level does not necessarily mean a person will develop gout.

While synovial fluid analysis remains the central pillar of diagnostic work up for all patients with new-onset acute monoarthritis, other laboratory investigations contribute to assist the diagnosis of gout, and in assessing comorbid conditions which affect gout.

• Uric acid level is only useful to assist with clinical diagnosis of gout in symptomatic individuals as hyperuricemia alone is not sufficient.
• It is less significant in diagnosing gout, especially during an acute attack when urate excretion through the kidneys is often increased.
• The levels are important during urate lowering therapy when the goal is to maintain a target urate level.

• Acute phase reactants, such as C-reactive protein, are usually increased during a flare—concentrations can be higher than 100 mg/L.^[4]
• Complete blood counts showing neutrophil leukocytosis can also be present depicting degree of systemic inflammation.^[5]

• Renal function tests are recommended when prescribing and monitoring drugs used for urate lowering therapy.

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