Why does gout cause a hot, red, swollen joint?

During a gout flare, urate crystals irritate the joint lining. Immune cells respond by releasing chemical signals that widen local blood vessels and draw fluid into the tissues. Increased blood flow can make the skin look red and feel hot, while fluid and inflammation cause swelling and stiffness. The joint may be extremely tender even with light touch. Most people with Gout notice hot, red, swollen joint during an acute flare, but similar changes can occur with infection, injury or other inflammatory arthritis.

Stop impact activity and rest the affected joint in a comfortable position. Elevation may reduce pressure from swelling, and a cool pack wrapped in cloth can offer temporary relief. Contact a healthcare professional for a treatment plan, particularly if the episode is new or symptoms are intense. Continue only medicines prescribed for you and follow their instructions; do not borrow someone else's gout medicine. Note when the symptoms began, which joint is involved and whether you have fever or a recent injury.

A hot, red, swollen joint with fever, chills or marked illness needs urgent medical assessment because infection can damage a joint and may look like gout. Seek prompt care if pain is severe, the joint cannot move, the limb is numb or pale, or symptoms began after trauma. A clinician may need an examination and joint-fluid testing before treatment is chosen.

Could this be infection as well as gout? Do I need joint-fluid testing? Which treatment should I use at the first warning sign? What symptoms mean I should attend urgent care?