A tophus specimen should be sent dry to the pathology department, and not be put in formalin.[notes 2]
Preferably make a touch prep for polarized light microscopy. At least if urate crystals are not initially detected, take sections to be put in 100% alcohol and tell the histology lab to prepare it as per gout protocol.[notes 2] With characteristic crystals on a touch prep, sections may possibly be submitted in formalin.[notes 2]
On a touch prep, look for needle-shaped crystals of urate. On polarized light, these will have negative birefriengence.
Uric acid crystals in polarized light, showing negative birefringence, with yellow color when aligned parallel to the axis of the red compensator, and blue when aligned perpendicularly to it.
- Bruce M Rothschild. Gout and Pseudogout Workup. Medscape. Updated: Jun 30, 2020