Diagnosis

The diagnosis is generally made on a clinical basis, although tests are required to confirm the disease.
Hyperuricemia is a common feature; however, urate levels are not always raised.

Hyperuricemia is defined as a plasma urate (uric acid) level greater than 420 μmol/L (7.0 mg/dL) in males (or 380 μmol/L in females); however, high uric acid level does not necessarily mean a person will develop gout. Additionally, urate is within the normal range in up to two-thirds of cases.

If gout is suspected, the serum urate test should be repeated once the attack has subsided. Other blood tests commonly performed are full blood count, electrolytes, renal function and erythrocyte sedimentation rate (ESR). This serves mainly to exclude other causes of arthritis, most notably septic arthritis.

A definitive diagnosis of gout is from light microscopy of joint fluid aspirated from the joint (this test may be difficult to perform) to demonstrate intracellular monosodium urate crystals in synovial fluid polymorphonuclear leukocytes. The urate crystal is identified by strong negative bi-refringence under polarised microscopy, and their needle-like morphology. A trained observer does better in distinguishing them from other crystals.