To help with diagnosis, a synovial fluid Gram stain and culture may be performed. Other conditions that can look similar include CPPD (pseudogout), rheumatoid arthritis, psoriatic arthritis, palindromic rheumatism, and reactive arthritis. Gouty tophi, in particular when not located in a joint, can be mistaken for basal cell carcinoma or other neoplasms. Prevention
Risk of gout attacks can be lowered by complete abstinence from drinking alcoholic beverages, reducing the intake of fructose (e.g. high fructose corn syrup) and purine-rich foods of animal origin, such as organ meats and seafood. Eating dairy products, vitamin C-rich foods, coffee, and cherries may help prevent gout attacks, as does losing weight. Gout may be secondary to sleep apnea via the release of purines from oxygen-starved cells. Treatment of apnea can lessen the occurrence of attacks. Medications
As of 2020, allopurinol is generally the recommended preventative treatment if medications are used. A number of other medications may occasionally be considered to prevent further episodes of gout, including probenecid, febuxostat, benzbromarone, and colchicine. Long term medications are not recommended until a person has had two attacks of gout, unless destructive joint changes, tophi, or urate nephropathy exist. It is not until this point that medications are cost-effective. They are not usually started until one to two weeks after an acute flare has resolved, due to theoretical concerns of worsening the attack.
Plain X-rays are usually normal and are not useful for confirming a diagnosis of early gout. They may show signs of chronic gout such as bone erosion. Synovial fluid
A definitive diagnosis of gout is based upon the identification of monosodium urate crystals in synovial fluid or a tophus. All synovial fluid samples obtained from undiagnosed inflamed joints by arthrocentesis should be examined for these crystals. Under polarized light microscopy, they have a needle-like morphology and strong negative birefringence. This test is difficult to perform and requires a trained observer. The fluid must be examined relatively soon after aspiration, as temperature and pH affect solubility. Blood tests
Hyperuricemia is a classic feature of gout, but nearly half of the time gout occurs without hyperuricemia and most people with raised uric acid levels never develop gout. Thus, the diagnostic utility of measuring uric acid levels is limited. Hyperuricemia is defined as a plasma urate level greater than 420 μmol/L (7.0 mg/dl) in males and 360 μmol/L (6.0 mg/dl) in females. Other blood tests commonly performed are white blood cell count, electrolytes, kidney function and erythrocyte sedimentation rate (ESR). However, both the white blood cells and ESR may be elevated due to gout in the absence of infection. A white blood cell count as high as 40.0×109/l (40,000/mm3) has been documented. Differential diagnosis
The most important differential diagnosis in gout is septic arthritis. This should be considered in those with signs of infection or those who do not improve with treatment.