Your doctor may remove some fluid from your swollen joint with a needle. This usually causes no more discomfort than a blood test. If urate crystals can be seen in the fluid under a microscope, you have gout. If calcium crystals are seen, you have a similar condition called pseudogout. The crystals formed when you have pseudogout aren't urate crystals-they are made of a calcium salt called calcium pyrophosphate. You may need to have an X-ray taken of your joint in order to rule out other conditions, but this is less common.
Attribution: BUPA