How is gout diagnosed?
A diagnosis of gout is often based on your symptoms and an examination of your joints, but your doctor may suggest you have some tests.
What tests are there for gout?
A blood test can measure the amount of urate in your blood. The critical serum level of urate (the saturation point) is around 360 μmo/L (equivalent to 6mg/dl). This is within the normal range for men, and for older women, so being informed that your blood test is ‘within normal limits’ is irrelevant – you need to know if it is above or below this critical level. A raised level of urate strongly supports a diagnosis of gout but can’t confirm it – not everyone with a raised level of urate will develop crystals in their joints, and it’s possible for urate levels in the blood to be normal at the time of an acute attack.
X-rays of joints will reveal joint damage if you have long-standing and poorly controlled gout. However, x-rays are rarely helpful in confirming the diagnosis because they’re usually normal in the early years of having gout. Ultrasound of joints can be used to detect earlier signs of gout, and can be useful where the diagnosis is uncertain.
Synovial fluid examinations involve taking fluid samples from a joint through a needle and examining them under a microscope for urate crystals. This test can confirm the diagnosis but isn’t always practical – it can be difficult and sometimes uncomfortable to draw fluid from a small joint such as the big toe. However, it may be possible to identify a few crystals in a sample taken from your knee, even if you’ve not yet had an attack of gout there. A fine needle inserted into a tophus under your skin can also be used to identify urate crystals.