The only certain way to diagnose gout, is if crystals of uric acid from a sample of joint fluid taken during an attack can be seen under a microscope. It is easy for a trained person to take a sample of joint fluid from a large swollen joint such as a knee, but this is often tricky or impossible if a small joint is affected, so doctors often have to assume that a diagnosis of gout is likely if there has been a typical attack of pain, swelling and redness in a joint, especially a big toe.

The diagnosis is easiest if a doctor can see and examine a red and swollen joint but it can help if you take a photograph of any swollen joint if there is likely to be a delay in being seen by a doctor.

During an attack of gout, uric acid levels in the blood can often be low or normal, so checking the uric acid levels in the blood during an attack is not helpful. Uric acid levels should be checked between attacks of gout to get a correct reading and if you have had a typical attack plus have high uric acid levels, the diagnosis of gout is very likely.