The breakdown product of purine (nucleotide) metabolism in the body is urate, most of the uric acid is not all eliminated by the kidneys, sometimes in the form of sodium urate in the blood circulation. In gout patients with high levels of sodium urate in the blood, excessive sodium urate is prone to urate deposition, which can lead to gout stones, synovitis, arthritis, kidney stones, etc. Most of the urate microscopically visible needle-like crystals are arranged in parallel with each other.

The staining solution adopts hexamine silver method to stain urate, which makes the urate crystals black, and is often used to assist in the diagnosis of ventilated nodules caused by urate, because urate is soluble in water and not easily soluble in ethanol, so when fixing, ethanol should be used instead of fixing solution such as formalin.