Diagnosis of gout usually begins with a physical examination and questions about personal and family medical history. A physician may suspect gout if a patient has had a history of acute arthritis, especially in big toe, that has been followed by a period when symptoms have disappeared.

To confirm gout as well as rule out other diseases with similar symptoms (e.g., pseudogout, septic arthritis, rheumatoid arthritis), a physician may perform an arthrocentesis. This procedure uses a needle to withdraw (aspirate) fluid from a joint so the sample can be examined for uric acid crystals. Gout crystals are needle-shaped and are negatively birefringent (unable to split a ray of light in two) under a polarized light microscope, as compared to pseudogout, where crystals are positively birefringent. During an acute attack, the crystals are often present inside white blood cells.

Large deposits of uric acid crystals (tophi) may be removed from beneath the skin in a biopsy to diagnose an advanced stage of gout called chronic tophaceous gout, though this procedure is not commonly performed for diagnosis.

Other tests may include:

• Urinalysis. Laboratory analysis of urine samples to measure the amount of uric acid being eliminated by the kidneys. This test is also performed to detect kidney stones.
  
  
• Blood tests. Laboratory analysis of blood samples to measure uric acid in the blood and detect hyperuricemia, which is present in most cases of gout. Hyperuricemia is defined as more than 7 milligrams of uric acid per deciliter of blood. However, some patients with gout may have normal levels of uric acid, so hyperuricemia is not used to definitively diagnose gout. Blood tests are also used to rule out other arthritic conditions.
  
  
• X-ray. This imaging test is primarily used to assess joint damage, especially in patients who have had multiple episodes of acute gouty arthritis.

Once a diagnosis has been made, treatment should be started immediately to avoid long-term complications of untreated gout, such as chronic tophaceous gout, kidney stones and kidney damage. Sometimes it becomes difficult to diagnose gout clinically, especially if it affects an atypical joint in the beginning and the person has normal values of uric acid.